code review 5697063: doc: improve go_for_cpp_programmers & contribute

doc/contribute.html

 <!--{
 "Title": "Contribution Guidelines"
 }-->
 
 <h2 id="Introduction">Introduction</h2>
 
 <p>
 This document explains how to contribute changes to the Go project.
 It assumes you have installed Go using the
 <a href="install.html">installation instructions</a> and
@@ skipping 120 matching lines @@
 
 <p>
 The code review server uses a Google Account to authenticate.
 (If you can use the account to
 <a href="https://www.google.com/accounts/Login?hl=en&amp;continue=http://www.goo gle.com/">sign in at google.com</a>,
 you can use it to sign in to the code review server.
 The email address you use on the Code Review site
 will be recorded in the <a href="http://code.google.com/p/go/source/list">Mercur ial change log</a>
 and in the <a href="/CONTRIBUTORS"><code>CONTRIBUTORS</code></a> file.
 You can <a href="https://www.google.com/accounts/NewAccount">create a Google Acc ount</a>
-associated with any address where you receive email.
+associated with any address where you receive email. If the following process 
+display invalid user name/password, try to·
+<a href="http://www.google.com/support/accounts/bin/static.py?hl=en&page=guide.c  s&guide=1056283&topic=1056286&rd=1">
+create a application-specific key</a>.
 </p>
 
 <pre>
 $ cd $GOROOT
 $ hg code-login
 Email (login for uploading to codereview.appspot.com): rsc@golang.org
 Password for rsc@golang.org:
 
 Saving authentication cookies to /Users/rsc/.codereview_upload_cookies_coderevie w.appspot.com
 </pre>
@@ skipping 370 matching lines @@
 This rigmarole needs to be done only for your first submission.
 </p>
 
 <p>Code that you contribute should use the standard copyright header:</p>
 
 <pre>
 // Copyright 2012 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 </pre>