feat: support special intro.md file

[GauBen]

Closes #31

[github-actions]

🦜 Chachalog

chachalog patch

• Introducing a new, special changelog entry: intro.md. (feat: support special intro.md file #41)

  If an intro.md file exists, it will be used to introduce the upcoming release of all packages to be released:

  <!-- intro.md -->
  # foo
  
  This major release...

  This line will be inserted in the CHANGELOG.md file for foo:

  <!-- foo/CHANGELOG.md -->
  # foo Changelog
  
  ## 2.0.0
  
  This major release...
  
  (rest of the changelog)

  See Introduce the ability to add a header in the release changelog #31 for the original feature request.

Create a new entry online or run npx chachalog@0.4.0 prompt to create a new entry locally.