doc/go1.22: document net/http/cgi changes

For #61422

Change-Id: If9c3d3ccbfb2061f42ffc26461209c96d38020e5
Reviewed-on: https://go-review.googlesource.com/c/go/+/556395
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Bryan Mills <bcmills@google.com>

doc/go1.22.html

@@ -747,13 +747,17 @@ <h3 id="minor_library_changes">Minor changes to the library</h3>
   </dd>
 </dl><!-- net/http -->
 
-<!-- <dl id="net/http/cgi"><dt><a href="/pkg/net/http/cgi/">net/http/cgi</a></dt> -->
-<!--   <dd> -->
-<!--     <p><\!-- CL 539615 -\-> -->
-<!--       TODO: <a href="https://go.dev/cl/539615">https://go.dev/cl/539615</a>: net/http/cgi: the PATH_INFO should be empty or start with a slash -->
-<!--     </p> -->
-<!--   </dd> -->
-<!-- </dl><\!-- net/http/cgi -\-> -->
+<dl id="net/http/cgi"><dt><a href="/pkg/net/http/cgi/">net/http/cgi</a></dt>
+  <dd>
+    <p><\!-- CL 539615 -\->
+      When executing a CGI process, the <code>PATH_INFO</code> variable is now
+      always set to the empty string or a value starting with a <code>/</code> character,
+      as required by RFC 3875. It was previously possible for some combinations of
+      <a href="/pkg/net/http/cgi#Handler.Root"><code>Handler.Root</code></a>
+      and request URL to violate this requirement.
+    </p>
+  </dd>
+</dl><\!-- net/http/cgi -\->
 
 <!-- <dl id="net/netip"><dt><a href="/pkg/net/netip/">net/netip</a></dt> -->
 <!--   <dd> -->