message: [skip ci] add a note on next_release.md file
diff: @@ -90,6 +90,8 @@ Because of `-u`, it will remember where you like to push this branch, and next t
  Possibly iterate a few times, add more commits and push them.
  ## Your pull request is ready
  +Do not forget to update `.github/next_release.md` to announce your development in the next release note.
  +
  Get your web browser to https://github.com/LOGIN/gudhi-devel, click on the button that says **Branch: some-name** (below the number of commits, above the list of files) and select the branch you are so proud of.
  Click on **New pull request** next to it.
  