docs: add semantic git commit messages

Author: mrholek

CONTRIBUTING.md

@@ -163,6 +163,18 @@ includes code changes) and under the terms of the
 [Creative Commons Attribution 3.0 Unported License](docs/LICENSE)
 (if it includes documentation changes).
 
+### Semantic Git commit messages
+
+Inspired by Sparkbox's awesome article on [semantic commit messages](http://seesparkbox.com/foundry/semantic_commit_messages). Please use following commit message format.
+
+* chore (updating npm tasks etc; no production code change) -> ```git test -m 'chore: commit-message-here'```
+* docs (changes to documentation) -> ```git commit -m 'docs: commit-message-here'```
+* feat (new feature) -> ```git commit -m 'feat: commit-message-here'```
+* fix (bug fix) -> ```git commit -m 'fix: commit-message-here'```
+* refactor (refactoring production code) -> ```git commit -m 'refactor: commit-message-here'```
+* style (formatting, missing semi colons, etc; no code change) -> ```git commit -m 'style: commit-message-here'```
+* test (adding missing tests, refactoring tests; no production code change) -> ```git test -m 'refactor: commit-message-here'```
+
 
 ## Code guidelines