Improve documentation post 1.0 release

[mockitoguy]

Suggested updates to the documentation post 1.0 release

• celebrating-contributors.md

  • document how can we skip getting contributors info from GitHub?

• version-bumps.md

  • document the plugin id and if it can be used standalone
  • document the task name and why it is useful to use
  • integration test with a project that only uses version bumps

• automated-release-notes.md

  • what tasks generate release notes
  • document that we push the release notes to GitHub and add github settings to the example. Link to the example project.
  • integration test with a project that only uses integration tests

• release-needed-plugin.md

  • document how comparing publications works
  • what tasks we can run to compare publications

• shipkit/CONTRIBUTING.md

  • update the document, try reading it from the standpoint of the user that
    • wants to submit first feature request or bug
    • wants to start a discussion (we guide in our documentation to open issues)