Add our preferred commit template to the repository. (apple#5)

Motivation:

We would like users to use the commit template across all
SwiftNIO projects, including this one.

Modifications:

Added the commit template to the repository.

Result:

The commit template will be in the repository.

dev/git.commit.template

@@ -0,0 +1,14 @@
+One line description of your change
+
+Motivation:
+
+Explain here the context, and why you're making that change.
+What is the problem you're trying to solve.
+
+Modifications:
+
+Describe the modifications you've done.
+
+Result:
+
+After your change, what will change.