Improved help for connect methods.

Prerequisites for all 3 methods are now bullet-pointed lists.
SSH now specifies that login details are needed as per ssh-slaves
plugin.
JNLP now specifies that slave.jar is needed.
JNLP's entrypoint argument help improved to make it clear that the
multi-line string needs to be expanded before being edited.
Example of custom command now mentions that it requires wget.
Also, moved details of the default setting to the bottom of the help
text.

src/main/resources/io/jenkins/docker/connector/DockerComputerAttachConnector/config.jelly

@@ -2,7 +2,18 @@
 <j:jelly xmlns:j="jelly:core" xmlns:st="jelly:stapler" xmlns:f="/lib/form">
 
     <f:block>
-        <span class="info">Prerequisites:</span> Docker image must have <a href="https://go.java">Java</a> installed. Also entrypoint must be able to accept jenkins slave connection parameters. <a href="https://github.com/jenkinsci/docker-jnlp-slave">See jenkins/docker-jnlp-slave as an example</a>
+        <span class="info">Prerequisites:</span>
+        <ul>
+            <li>
+                Docker image must have <a href="https://go.java">Java</a> installed.
+            </li>
+            <li>
+                Entrypoint must be able to accept jenkins slave connection parameters.
+                See 
+                <a href="https://github.com/jenkinsci/docker-jnlp-slave">jenkins/docker-jnlp-slave</a>
+                as an example.
+            </li>
+        </ul>
     </f:block>
 
     <f:entry title="${%User}" field="user">

src/main/resources/io/jenkins/docker/connector/DockerComputerJNLPConnector/config.jelly

@@ -2,8 +2,18 @@
 <j:jelly xmlns:j="jelly:core" xmlns:st="jelly:stapler" xmlns:f="/lib/form">
 
     <f:block>
-        <span class="info">Prerequisites:</span> Docker image must have <a href="https://go.java">Java</a> installed,
-        and Jenkins master has to be accessible over network <em>from</em> container.
+        <span class="info">Prerequisites:</span>
+        <ul>
+            <li>
+                Jenkins master has to be accessible over network <em>from</em> the container.
+            </li>
+            <li>
+                Docker image must have <a href="https://go.java">Java</a> installed.
+            </li>
+            <li>
+                Docker image must <em>either</em> have <tt>slave.jar</tt> pre-installed <em>or</em> have its entry point code download it.
+            </li>
+        </ul>
     </f:block>
 
     <f:entry title="${%User}" field="user">
@@ -15,7 +25,7 @@
     </f:entry>
 
     <f:entry title="${%EntryPoint Arguments}" field="entryPointArgumentsString">
-      <f:expandableTextbox />
+        <f:expandableTextbox />
     </f:entry>
 
     <f:property field="jnlpLauncher"/>

src/main/resources/io/jenkins/docker/connector/DockerComputerJNLPConnector/help-entryPointArgumentsString.jelly

@@ -3,7 +3,15 @@
   <div>
     <p>
       Arguments to be passed to the container's entry point.
+    </p>
+    <p>
+      <b>NOTE:</b>
+      This field is a multi-line string.
       Each (non-empty) line defines a seperate argument.
+      If you require more than one argument
+      (e.g. copying one of the examples below)
+      then you will need to expand the field,
+      otherwise you'll end up with one long line instead of multiple lines.
     </p>
     <p>
       Limited variable substitution (using $${VARIABLE_NAME} syntax) is carried out on the configured strings prior to starting the container.
@@ -15,22 +23,31 @@
         </j:forEach>
       </dl>
     </p>
+    <p>
+      For example, if you are using a custom container that has
+      <tt>java</tt>
+      and
+      <tt>wget</tt>
+      installed but does not have
+      <tt>slave.jar</tt>
+      pre-installed then you could use the following instead:
+      <blockquote>
+        <tt>sh</tt><br/>
+        <tt>-c</tt><br/>
+        <tt>wget $${JENKINS_URL}jnlpJars/slave.jar &amp;&amp; java -jar slave.jar -jnlpUrl $${JENKINS_URL}computer/$${NODE_NAME}/slave-agent.jnlp -secret $${JNLP_SECRET}</tt><br/>
+      </blockquote>
+    </p>
     <p>
       If this field is left blank then it defaults to arguments
       suitable for the standard
       Jenkins JNLP Agent Docker image, 
-      <a href="https://github.com/jenkinsci/docker-jnlp-slave">jenkins/jnlp-slave</a>, namely:
+      <a href="https://github.com/jenkinsci/docker-jnlp-slave">jenkins/jnlp-slave</a>,
+      which are:
       <blockquote>
         <j:forEach var="entry" items="${app.getDescriptor('io.jenkins.docker.connector.DockerComputerJNLPConnector').defaultEntryPointArguments}">
           <tt>${entry}</tt><br/>
         </j:forEach>
       </blockquote>
-      If you are using a custom container that does not use the same entry point then you could use the following arguments instead:
-      <blockquote>
-        <tt>sh</tt><br/>
-        <tt>-c</tt><br/>
-        <tt>wget $${JENKINS_URL}jnlpJars/slave.jar &amp;&amp; java -jar slave.jar -jnlpUrl $${JENKINS_URL}computer/$${NODE_NAME}/slave-agent.jnlp -secret $${JNLP_SECRET}</tt><br/>
-      </blockquote>
     </p>
   </div>
 </j:jelly>

src/main/resources/io/jenkins/docker/connector/DockerComputerSSHConnector/config.jelly

@@ -2,7 +2,30 @@
 <j:jelly xmlns:j="jelly:core" xmlns:st="jelly:stapler" xmlns:f="/lib/form" >
 
     <f:block>
-        <span class="info">Prerequisites:</span> Docker image must have <a href="https://www.openssh.com/">sshd</a> and a JDK installed.
+        <span class="info">Prerequisites:</span>
+        <ul>
+            <li>
+                The docker container's mapped SSH port,
+                typically a port on the docker host,
+                has to be accessible over network <em>from</em> the master.
+            </li>
+            <li>
+                Docker image must have
+                <a href="https://www.openssh.com/">sshd</a>
+                installed.
+            </li>
+            <li>
+                Docker image must have
+                <a href="https://go.java">Java</a>
+                installed.
+            </li>
+            <li>
+                Log in details configured as per
+                <a href="https://plugins.jenkins.io/ssh-slaves">ssh-slaves</a>
+                plugin.
+            </li>
+        </ul>
+
     </f:block>
 
     <f:dropdownDescriptorSelector  title="SSH key" field="sshKeyStrategy" />