[clang] [TySan] Add initial documentation for Type Sanitizer (PR #123595)

[Erich Keane via cfe-commits]

================
@@ -0,0 +1,156 @@
+================
+TypeSanitizer
+================
+
+.. contents::
+   :local:
+
+Introduction
+============
+
+TypeSanitizer is a detector for strict type aliasing violations. It consists of a compiler
+instrumentation module and a run-time library. The tool detects violations where you access 
----------------
erichkeane wrote:

`violations` of what?  Would love another sentence or two here just explaining what it is detecting better.  Something like (please don't use unless it is correct!):

"This tool detects violations of the strict-aliasing rule, which prohibits access of a memory location as a type that is different from the dynamic type of the object at that location."

Or something?  

https://github.com/llvm/llvm-project/pull/123595