Mention creation of GitHub release in ReleaseProcess.md

[Marcono1234]

Purpose

Update ReleaseProcess.md because it was outdated

Description

• Remove mention of having to update CHANGELOG.md (see Mention in CHANGELOG that GitHub Releases are used in the future #2230)
• Mention that GitHub release should be created

Also updates the README to first point to the GitHub releases

Checklist

• New code follows the Google Java Style Guide
• If necessary, new public API validates arguments, for example rejects null
• New public API has Javadoc
  • Javadoc uses @since $next-version$
    ($next-version$ is a special placeholder which is automatically replaced during release)
• If necessary, new unit tests have been added
  • Assertions in unit tests use Truth, see existing tests
  • No JUnit 3 features are used (such as extending class TestCase)
  • If this pull request fixes a bug, a new test was added for a situation which failed previously and is now fixed
• mvn clean verify javadoc:jar passes without errors

[eamonnmcmanus]

LGTM. Thanks!