[llvm] [Docs][llvm-exegesis] Add documentation on recently added options (PR #75408)

[Clement Courbet via llvm-commits]

================
@@ -81,6 +81,12 @@ properly.
   definition should start at. Note that a single memory definition can be
   mapped multiple times. Using this annotation requires the subprocess
   execution mode.
+* `LLVM-EXEGESIS-SNIPPET-ADDRESS <address>` - This annotation allows for
+  setting the address where the beginning of the snippet to be executed will
+  be mapped in at. The address is given in hexadecimal. Note that the snippet
+  also includes setup code, so the instruction exactly at the specified
+  address will not be the first instruction in the snippet. Using this
+  annotation requires the subprocess execution mode.
----------------
legrosbuffle wrote:

Maybe explain why this would be useful (RIP-relative addressing)

https://github.com/llvm/llvm-project/pull/75408