[compiler-rt] [llvm] [docs][IRPGO]Document two binary formats for IRPGO profiles (PR #76105)

[David Li via llvm-commits]

================
@@ -0,0 +1,387 @@
+=====================
+IRPGO Profile Format
----------------
david-xl wrote:

IRPGO --> Instrumentation PGO. Note that Frontend PGO uses the same format.

https://github.com/llvm/llvm-project/pull/76105