[annotations] Add a README with a build instruction for maven
[annotations] Add a README with a build instruction for maven

Summary:
Although, we have Makefile and BUCK build def, this is a maven project
which is supposed to be released to Maven Central, so it's worth
having a short instruction on how to build it with maven.

Reviewed By: mityal

Differential Revision: D18037109

fbshipit-source-id: 6aebf4384

facebook/infer,jvillard/infer,facebook/infer,facebook/infer,jvillard/infer,facebook/infer,jvillard/infer,facebook/infer,facebook/infer,jvillard/infer,jvillard/infer,jvillard/infer,jvillard/infer,facebook/infer