Update CONTRIBUTING.md

Add some info about commit subject prefixes.

1 files changed, 10 insertions, 1 deletions

diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index c370f9304..c35544cae 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -85,7 +85,16 @@ To make the contribution process as seamless as possible, we ask for the followi
 
 This [blog article](http://chris.beams.io/posts/git-commit/) is a good resource for learning how to write good commit messages,
 the most important part being that each commit message should have a title/subject in imperative mood starting with a capital letter and no trailing period:
-*"Return error on wrong use of the Paginator"*, **NOT** *"returning some error."*
+*"js: Return error when option x is not set"*, **NOT** *"returning some error."*
+
+Most title/subjects should have a lower-cased prefix with a colon and one whitespace. The prefix can be:
+
+* The name of the package where (most of) the changes are made (e.g. `media: Add text/calendar`)
+* If the package name is deeply nested/long, try to shorten it from the left side, e.g. `markup/goldmark` is OK, `resources/resource_transformers/js` can be shortened to `js`.
+* If this commit touches several packages with a common functional topic, use that as a prefix, e.g. `errors: Resolve correct line numbers`)
+* If this commit touches many packages without a common functional topic, prefix with `all:` (e.g. `all: Reformat Go code`)
+* If this is a documentation update, prefix with `docs:`.
+* If nothing of the above applies, just leave the prefix out.
 
 Also, if your commit references one or more GitHub issues, always end your commit message body with *See #1234* or *Fixes #1234*.
 Replace *1234* with the GitHub issue ID. The last example will close the issue when the commit is merged into *master*.