[Docs] [llvm-mca] Point out a caveat for using llvm-mca markers in source code.
Summary: See: https://bugs.llvm.org/show_bug.cgi?id=42173
Reviewers: andreadb, mattd, RKSimon, spatel
Reviewed By: andreadb
Subscribers: tschuett, gbedwell, llvm-commits, andreadb
Tags: #llvm
Patch by Max Marrone (maxpm)! Thanks!
Differential Revision: https://reviews.llvm.org/D63040
llvm-svn: 362979