doc/go1.18: cite CLs for more efficient scavenging

For #47694.

Change-Id: Ic6088b1811600670a57f28426f4158a7c7517c82
Reviewed-on: https://go-review.googlesource.com/c/go/+/369616
Trust: Austin Clements <[email protected]>
Reviewed-by: Michael Knyszek <[email protected]>

Author: aclements

doc/go1.18.html

@@ -282,7 +282,7 @@ <h2 id="runtime">Runtime</h2>
   <code>GOGC</code> where necessary.
 </p>
 
-<p>
+<p><!-- CL 358675, CL 353975, CL 353974 -->
   The runtime now returns memory to the operating system more efficiently and has
   been tuned to work more aggressively as a result.
 </p>