Set up a bot to track signing of CLA

[0b10011]

If signing the CLA is required for contributors, I would recommend setting up a bot that either warns about not having signed the CLA, or having a buildbot set up that only merges after the CLA has been signed.

For example, node warns with an automatic comment: nodejs/node-v0.x-archive#5491 (comment)

[ingorichter]

We only have this functionality for building brackets itself. Travis will build branches and checks if the contributor signed the CLA and fails the build if this is not the case. But we don't have this for the other repos. This is a good feature request for all our other repos. Thanks.