update README.md for testing and release mvn commands

[stevehu]

For normal testing, there is no need to build src.jar and doc.jar as well as the fat.jar as they take a lot of time. You can just run mvn clean install exec:exec to start the server. When you are planning to release, you can run mvn clean install -Prelease to build all artifacts.

The above information should be in the README.md of each generated project.

[stevehu]

Need more information in the README.md to guide users on how to start the project from the scaffolded project. Possible linking to some documents or videos.

How to run unit test, integration test. How to start the server in test mode. How to release the server. How to enable some of the handlers etc.