[clang-tidy] add_new_check.py improvements: add doc file, refer it from .h
[clang-tidy] add_new_check.py improvements: add doc file, refer it from .h

+ some console logging and minor cleanups.


git-svn-id: a34e9779ed74578ad5922b3306b3d80a0c825546@247282 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/clang-tools-extra,llvm-mirror/clang-tools-extra,llvm-mirror/clang-tools-extra,llvm-mirror/clang-tools-extra