Documentation: Rephrase header

We are talking about commits here now, not just about description.

At the same time make the first occurence of "the commit" to
"each commit" so readers don't get irritated by the wrong
grammatical number.

Documenation/SubmittingPatches.md

@@ -1,12 +1,12 @@
 Here are some guidelines for people who want to make changes
 to this repository.
 
-Describe your changes well.
-===========================
+Commits
+=======
 
 Make separate commits for logically separate changes.
 
-The first line of the commit message should be a short description (50
+The first line of each commit message should be a short description (50
 characters is the soft limit, see DISCUSSION in git-commit(1)), and
 should skip the full stop.  It is also conventional in most cases to
 prefix the first line with "project: " where the project is a filename
@@ -64,6 +64,7 @@ changes do not trigger errors with the sample pre-commit hook shipped
 in templates/hooks--pre-commit.  To help ensure this does not happen,
 run git diff --check on your changes before you commit.
 
+
 Publish your work in a separate branch.
 =======================================