message: Update contributing to be more helpful around changelog entries
diff: @@ -38,8 +38,10 @@ This project follows "git flow" semantics. In practice, this means:
  `npm run check`.
  - Create a pull request. If this PR fixes an issue, link to it by referring to its number.
  - PRs from community members must be signed off as per Synapse's [Attribution section](https://github.com/matrix-org/synapse/blob/master/CONTRIBUTING.rst#attribution)
  - - Create a changelog entry in `changelog.d`. A changelog filename should be `${GithubIssueNumber}.{bugfix|misc|feature|doc|removal}`
  + - Create a changelog entry in `changelog.d`. A changelog filename should be `${GithubPRNumber}.{bugfix|misc|feature|doc|removal}`
  The change should include information that is useful to the user rather than the developer.
  + You can choose to sign your changelog entry to be credited by appending something like "Thanks to @Half-Shot"
  + at the end of the file, on the same line.
  ## Coding notes
  The IRC bridge is compatible on Node.js v10+. Buildkite is used to ensure that tests will run on
  