doc/help: tweak descriptions, make official channels clearer

Change-Id: I5c8df05a25421489ec5122de85dbda756483c536
Reviewed-on: https://go-review.googlesource.com/34289Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

doc/help.html

@@ -11,6 +11,9 @@
 
 <h3 id="mailinglist"><a href="https://groups.google.com/group/golang-nuts">Go Nuts Mailing List</a></h3>
 <p>
+Get help from Go users, and share your work on the official mailing list.
+</p>
+<p>
 Search the <a href="https://groups.google.com/group/golang-nuts">golang-nuts</a>
 archives and consult the <a href="/doc/go_faq.html">FAQ</a> and
 <a href="//golang.org/wiki">wiki</a> before posting.
@@ -18,12 +21,12 @@ archives and consult the <a href="/doc/go_faq.html">FAQ</a> and
 
 <h3 id="forum"><a href="https://forum.golangbridge.org/">Go Forum</a></h3>
 <p>
-The <a href="https://forum.golangbridge.org/">Go Forum</a> is an alternate discussion
+The <a href="https://forum.golangbridge.org/">Go Forum</a> is a discussion
 forum for Go programmers.
 </p>
 
 <h3 id="slack"><a href="https://blog.gopheracademy.com/gophers-slack-community/">Gopher Slack</a></h3>
-<p>Get live support from the official Go slack channel.</p>
+<p>Get live support from other users in the Go slack channel.</p>
 
 <h3 id="irc"><a href="irc:irc.freenode.net/go-nuts">Go IRC Channel</a></h3>
 <p>Get live support at <b>#go-nuts</b> on <b>irc.freenode.net</b>, the official