doc/go1.18: document non-cooperative preemption on windows/arm{,64}

For #47694.
Updates #49759.

Change-Id: I7accd81b8ea6c31e4a2b5e155cf93fe9c447813b
Reviewed-on: https://go-review.googlesource.com/c/go/+/367095
Trust: Jason A. Donenfeld <[email protected]>
Reviewed-by: Emmanuel Odeke <[email protected]>

Author: zx2c4

doc/go1.18.html

@@ -193,8 +193,11 @@ <h3 id="gofmt"><code>gofmt</code></h3>
 
 <h2 id="runtime">Runtime</h2>
 
-<p>
-  TODO: complete this section, or delete if not needed
+<p><!-- https://golang.org/issue/49759 -->
+  The <pre>windows/arm</pre> and <pre>windows/arm64</pre> ports now support
+  non-cooperative preemption, bringing that capability to all four Windows
+  ports, which should hopefully address subtle bugs encountered when calling
+  into Win32 functions that block for extended periods of time.
 </p>
 
 <h2 id="compiler">Compiler</h2>