[Polly][docs][Release Notes] Adding Information about Remarks to Release Notes and Documentation

Summary: Based off of D35399

Reviewers: pollydev, llvm-commits, bollu, grosser

Reviewed By: grosser

Tags: #polly

Contributed-by: Tarun Ranjendran

Differential Revision: https://reviews.llvm.org/D35596

llvm-svn: 308403