Update CONTRIBUTING.adoc

substrate/CONTRIBUTING.adoc

@@ -10,7 +10,7 @@ Individuals making significant and valuable contributions are given commit-acces
 
 There are a few basic ground-rules for contributors (including the maintainer(s) of the project):
 
-. **No `--force` pushes** or modifying the Git history in any way. If you need to rebase, ensure you do it in your own repo.
+. **No `--force` pushes** or modifying the master branch history in any way. If you need to rebase, ensure you do it in your own repo.
 . **Non-master branches**, prefixed with a short name moniker (e.g. `gav-my-feature`) must be used for ongoing work.
 . **All modifications** must be made in a **pull-request** to solicit feedback from other contributors.
 . A pull-request *must not be merged until CI* has finished successfully.