Add more detail to release process

[seanbudd]

Link to issue number:

Relates to nvaccess/addon-datastore-validation#33

Summary of the issue:

Information was lacking on the stability of the add-on API and translation strings at various stages of the release process.
This makes the work required or expected for add-on developers and translators unclear.

Description of user facing changes

Expands release process to include more information for translators and add-on developers.

[AppVeyorBot]

• PASS: Translation comments check.
• PASS: Unit tests.
• PASS: Lint check.
• FAIL: System tests (tags: installer NVDA). See test results for more information.
• Build (for testing PR): https://ci.appveyor.com/api/buildjobs/sm5sbvre3x9i29wr/artifacts/output/nvda_snapshot_pr15607-29588,8ab6d754.exe
• CI timing (mins):
  INIT 0.0,
  INSTALL_START 0.9,
  INSTALL_END 1.0,
  BUILD_START 0.0,
  BUILD_END 23.7,
  TESTSETUP_START 0.0,
  TESTSETUP_END 0.3,
  TEST_START 0.0,
  TEST_END 5.0,
  FINISH_END 0.1

See test results for failed build of commit 8ab6d7545f