doc/go1.18: add Clone doc

For golang#47694

Change-Id: I3b135f6ff199d7a9746726b131fbe7dd97a8e95e
Reviewed-on: https://go-review.googlesource.com/c/go/+/364254
Reviewed-by: Dmitri Shuralyov <[email protected]>
Trust: Heschi Kreinick <[email protected]>

Author: 180909

doc/go1.18.html

@@ -439,7 +439,9 @@ <h3 id="minor_library_changes">Minor changes to the library</h3>
 <dl id="strings"><dt><a href="/pkg/strings/">strings</a></dt>
   <dd>
     <p><!-- CL 345849 -->
-      TODO: <a href="https://golang.org/cl/345849">https://golang.org/cl/345849</a>: add Clone function
+      The new <a href="/pkg/strings/#Clone"><code>Clone</code></a> function copies the input
+      <code>string</code> without the returned cloned <code>string</code> referencing
+      the input string's memory.
     </p>
 
     <p><!-- CL 332771 -->