[PR template] Add reminder to add/modify/remove unit tests as appropr…

…iate (#708)

.github/PULL_REQUEST_TEMPLATE.md

@@ -6,7 +6,11 @@ https://github.com/Azure/SONiC/blob/gh-pages/CONTRIBUTING.md
 
 If this is a bug fix, make sure your description includes "closes #xxxx",
 "fixes #xxxx" or "resolves #xxxx" so that GitHub automatically closes the related
-issue when the PR is merged
+issue when the PR is merged.
+
+If you are adding/modifying/removing any command or utility script, please also
+make sure to add/modify/remove any unit tests from the sonic-utilities-tests
+directory as appropriate.
 
 If you are modifying or removing an existing 'show', 'config' or 'sonic-clear'
 subcommand, or you are adding a new subcommand, please make sure you also
@@ -26,5 +30,3 @@ Please provide the following information:
 
 **- New command output (if the output of a command-line utility has changed)**
 
--->
-