README: use docs/rel-notes/ for the release notes

README.md

@@ -125,7 +125,7 @@ How Can I Contribute?
 
 Fork libgit2/libgit2 on GitHub, add your improvement, push it to a branch
 in your fork named for the topic, send a pull request. If you change the
-API or make other large changes, make a note of it in docs/RelNotes/ in a
+API or make other large changes, make a note of it in docs/rel-notes/ in a
 file named after the next release.
 
 You can also file bugs or feature requests under the libgit2 project on