Improvement ideas to release process

[balopat]

Description of the issue

During the last release these were some items we thought about with @tanujkhattar to improve:

• separate minor/major from patch workflow
• explain pypi / twine better - pip install pypi seems missing
• python -m pip install --index-url https://test.pypi.org/simple/ --extra-index-url https://pypi.org/simple your-package
• change the password situation
  • https://stackoverflow.com/questions/57935191/twine-is-asking-for-my-password-each-time-how-to-use-the-pypirc
• verify package installs its own pytest
• if you need to rebuild things during verification, use the build number hack: https://github.com/pypa/packaging-problems/issues/74#issuecomment-693987158
• commits since last release - git log "--pretty=%h %s" v0.9.1..HEAD
• PRs with breaking changes:
  • is:pr is:closed label:"BREAKING CHANGE" merged:>2020-10-01
  • label is great but we should mandate the specific release note summary in the PR description (automerge bot / github actions check?)
    • major changes - label them and mandate release note summary
• bump master to next dev version should be in the same PR as the notebooks

[dstrain115]

@MichaelBroughton Do you want to weigh in? I do not think this is needed before Cirq 1.0, especially if we revamp release process after Cirq 1.0. I am removing the before 1.0 tag unless you have objections.