doc/go1.1.html: add a note about additional platforms

Mention support for NetBSD, OpenBSD, and cgo for linux/arm.

R=golang-dev, dvyukov, r, minux.ma, adg, bradfitz, adg
CC=golang-dev
https://golang.org/cl/8152043

doc/go1.1.html

@@ -352,6 +352,17 @@ To update pre-Go 1 code to Go 1.1, use a Go 1.0 tool chain
 to convert the code to Go 1.0 first.
 </p>
 
+<h3 id="platforms">Additional platforms</h3>
+
+<p>
+The Go 1.1 tool chain adds experimental support for <code>freebsd/arm</code>,
+<code>netbsd/386</code>, <code>netbsd/amd64</code>, <code>netbsd/arm</code>, 
+<code>openbsd/386</code> and <code>openbsd/amd64</code> platforms.
+<code>freebsd/arm</code> and <code>netbsd/arm</code> require an ARMv6 or
+better processor. Go 1.1 adds experimental support for <code>cgo</code> on
+<code>linux/arm</code>.
+</p>
+
 <h2 id="performance">Performance</h2>
 
 <p>