doc(contribute): add link to Deprecation and Archiving Policy (#1403)

Author: erisu

www/contribute/index.html

@@ -17,8 +17,9 @@ <h1>Want to Contribute?</h1>
     <div class="col-sm-7">
         <h2>What you can do</h2>
         <ul class="contribute-get-started-steps">
-            <li>File a <a href="./issues.html">bug or task</a></li>
-            <li>Read the <a href="./contribute_guidelines.html">Contributor Guidelines</a></li>
+            <li>File a <a href="{{ site.baseurl }}/contribute/issues.html">bug or task</a></li>
+            <li>Read the <a href="{{ site.baseurl }}/contribute/contribute_guidelines.html">Contributor Guidelines</a></li>
+            <li>Read the <a href="{{ site.baseurl }}/deprecation_policy.html">Deprecation and Archiving Policy</a></li>
             <li>Join the <a href="{{ site.baseurl }}/contact">Dev mailing list</a> and send a brief introduction of yourself to it</li>
             <li>Join the discussion on <a href="https://s.apache.org/cordova-slack">Slack</a></li>
             <li>Try out the next version of Cordova using <a href="{{ site.baseurl }}/contribute/nightly_builds.html">nightly builds</a></li>
@@ -33,7 +34,7 @@ <h2>What you can do</h2>
                 </li>
                 <li>
                     <span class="glyphicon glyphicon-user"></span><i>&nbsp;</i>
-                    See all <a href="./team.html">Team</a>
+                    See all <a href="{{ site.baseurl }}/contribute/team.html">Team</a>
                 </li>
             </ul>
         </div>