doc/go1.10: note that netbsd/arm is definitely broken

Remove the ambiguity, know that we know it's actually broken,
per https://github.com/golang/go/issues/23073#issuecomment-351045421

Updates #23073

Change-Id: I9b904da2f4c7105a0727d2a9056aaa6895d3dadc
Reviewed-on: https://go-review.googlesource.com/83856Reviewed-by: Ian Lance Taylor <iant@golang.org>

doc/go1.10.html

@@ -77,8 +77,8 @@ support for FreeBSD 9.3 has been removed.
 
 <p id="netbsd">
 Go now runs on NetBSD again but requires the unreleased NetBSD 8.
-Only <code>GOARCH</code> <code>amd64</code> and <code>386</code> are
-known to work. The <code>arm</code> port might work but is untested.
+Only <code>GOARCH</code> <code>amd64</code> and <code>386</code> have
+been fixed. The <code>arm</code> port is still broken.
 </p>
 
 <p id="openbsd">