[clang-tidy] Add a note about modernize-replace-random-shuffle

Summary:
This adds a note warning the users that the way the suggested fix seeds the
random number generator is poor.

Reviewers: hokein

Reviewed By: hokein

Subscribers: cfe-commits, xazax.hun

Differential Revision: https://reviews.llvm.org/D39787

llvm-svn: 317689