update plugin readme
update plugin readme

readme update

Testing Done:
new view can be seen at https://github.com/wisechengyi/intellij-pants-plugin/blob/readme_update/README.md#running-plugin-tests-with-pants

https://travis-ci.org/wisechengyi/intellij-pants-plugin/builds/93248338

Bugs closed: 75

Reviewed at https://rbcommons.com/s/twitter/r/3180/

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