Apply suggestions from code review

Co-authored-by: Loïc Huder <[email protected]>

CONTRIBUTING.md

@@ -62,8 +62,10 @@ The new tag will trigger the CI (`release.yml`) that will build and release the
 
 Release notes can then be written in the [Releases page](https://github.com/silx-kit/h5grove/releases).
 
+### Pre-releases
+
 The following commands can be used to handle the pre-release cycle:
-- To tag the first pre-release, run `bump2version --new-release <X.Y.Zb0> [patch|minor|major]`
+- To tag the first pre-release, run `bump2version --new-version <X.Y.Zb0> [patch|minor|major]` where `X.Y.Z` is the version number of the next release
 - To bump the pre-release number, run `bump2version pre`
 - To bump to the release, run `bump2version prerelease`