Add CONTRIBUTING.md with git commit message guides

CONTRIBUTING.md

+# Styleguides
+
+### Git Commit Messages
+
+* Use the present tense (`Add feature` instead of `Added feature`)
+* Use the imperative mood (`Move cursor to...`instead of `Moves cursor to...`)
+* Limit the first line to 72 characters or less
+* Reference issues and merge requests liberally after the first line