Merge pull request JanusGraph#341 from robertdale/skip_ci [skip ci]

Added note about adding [skip ci] to documentation changes. [skip ci]

CONTRIBUTING.md

@@ -127,6 +127,19 @@ you've signed the contribution.
 > `git ci -v` will get you a diff of your commit while writing your commit
 > message.
 
+> Note: If this is a non-code change, e.g. documentation, add `[skip ci]` to the
+> PR subject line. This is to save CPU time on Travis CI, which lets us get more
+> build time for the other changes which actually change the code.
+>
+> The tests actually run twice for each PR:
+> 
+> * when the PR is submitted for review
+> * when the PR is merged to the base branch
+>
+> Having [skip ci] in the commit skips the first one, but the merge commit also
+> needs it, so having it in the title (first line of commit) helps it easily
+> propagate to both places.
+
 ## Push your changes to your GitHub fork
 
 ```bash