doc: mention improvements in checking R15 use in assembly when dynamic linking

Change-Id: I223649818763c0620875c034a77a8865252e3e69
Reviewed-on: https://go-review.googlesource.com/c/go/+/499280
Reviewed-by: Keith Randall <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>
TryBot-Bypass: Keith Randall <[email protected]>

Author: randall77

doc/go1.21.html

@@ -222,6 +222,13 @@ <h2 id="compiler">Compiler</h2>
   TODO: complete this section, or delete if not needed
 </p>
 
+<h2 id="assembler">Assembler</h2>
+
+<!-- CL 476295 -->
+<p>
+  The verifier that checks for incorrect uses of <code>R15</code> when dynamic linking on amd64 has been improved.
+</p>
+
 <h2 id="linker">Linker</h2>
 
 <!-- CL 457455 -->