Add some comments to the YouCompleteMe changes.

* .ycm_extra_conf.py: Add header mentioning the source and copyright.

* Makefile.in: Comment explaining purpose of compile-commands target.

Suggested by: julianf


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1476416 13f79535-47bb-0310-9956-ffa450edef68