doc: document new math.Fma function

This accidentally got committed - please review the whole paragraph
as if it was new.

Change-Id: I98e1db4670634c6e792d26201ce0cd329a6928b6
Reviewed-on: https://go-review.googlesource.com/c/go/+/202579
Reviewed-by: Ian Lance Taylor <iant@golang.org>

doc/go1.14.html

@@ -225,12 +225,11 @@ <h2 id="library">Core library</h2>
 <dl id="math"><dt><a href="/pkg/math/">math</a></dt>
   <dd>
     <p><!-- CL 127458 -->
-      The new <a href="/pkg/math/#Fma"><code>Fma</code></a> function
+      The new <a href="/pkg/math/#FMA"><code>FMA</code></a> function
       computes <code>x*y+z</code> in floating point with no
       intermediate rounding of the <code>x*y</code>
       computation. Several architectures implement this computation
-      using dedicated hardware instructions for additional
-      performance.
+      using dedicated hardware instructions for additional performance.
     </p>
 
 </dl><!-- math -->