doc/go1.10: add NetBSD and OpenBSD to Go 1.10 release notes

Fixes #22911

Change-Id: I61de85323e290b64917a09bc512935e835ff7cf0
Reviewed-on: https://go-review.googlesource.com/82276Reviewed-by: Ian Lance Taylor <iant@golang.org>

doc/go1.10.html

@@ -75,6 +75,18 @@ Go 1.10 now requires FreeBSD 10.3 or later;
 support for FreeBSD 9.3 has been removed.
 </p>
 
+<p id="netbsd">
+Go now runs on NetBSD again, but requires the unreleased NetBSD 8.
+Only <code>GOARCH=amd64</code> running on NetBSD amd64 and <code>GOARCH=386</code>
+running on NetBSD i386 are known to work. 64-bit Go binaries are known to
+fail on 32-bit NetBSD kernels. <code>GOARCH=arm</code> is untested.
+</p>
+
+<p id="openbsd">
+Go 1.10 is the last release that will run on OpenBSD 6.0.
+Go 1.11 will require OpenBSD 6.2.
+</p>
+
 <p id="mips">
 On 32-bit MIPS systems, the new environment variable settings
 <code>GOMIPS=hardfloat</code> (the default) and