doc/go1.15: add release notes for fmt

Updates #37419

Change-Id: I344dd93ed7a75f88e7f937c80f5a6ad6c0327a07
Reviewed-on: https://go-review.googlesource.com/c/go/+/236417
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>

doc/go1.15.html

diff --git a/doc/go1.15.html b/doc/go1.15.html
index 492cac0..ea96dcf 100644
--- a/doc/go1.15.html
+++ b/doc/go1.15.html
@@ -390,7 +390,8 @@
 <dl id="fmt"><dt><a href="/pkg/fmt/">fmt</a></dt>
   <dd>
     <p><!-- CL 215001 -->
-      TODO: <a href="https://golang.org/cl/215001">https://golang.org/cl/215001</a>: do not remove trailing zeros for %g and %G with #(sharp) flag
+      The printing verbs <code>%#g</code> and <code>%#G</code> now preserve
+      trailing zeros for floating-point values.
     </p>
   </dd>
 </dl><!-- fmt -->