Add a contributing section with Help Wanted hotlist

This type of information has a different lifecycle than the
source-code and is better suited on the homepage than in the
documentation.

Feature: Issue 40015541
Change-Id: I65a0f4ee8813d743faf2704ed653931c35753d76

_data/topnav.yml

@@ -22,7 +22,7 @@ topnav_dropdowns:
         - title: Members
           url: /members.html
         - title: Contributing
-          external_url: https://gerrit-documentation.storage.googleapis.com/Documentation/3.9.1/dev-community.html#how-to-contribute
+          url: /contributing.html
         - title: Fixing a bug
           url: /bug-fixing.html
         - title: Presentations

pages/site/community/contributing.md

@@ -0,0 +1,29 @@
+---
+title: "Contributing"
+permalink: contributing.html
+hide_sidebar: true
+hide_navtoggle: true
+toc: false
+---
+
+## Contributing
+
+### How can I contribute?
+
+The [How To Contribute](https://gerrit-documentation.storage.googleapis.com/Documentation/3.9.1/dev-community.html#how-to-contribute)
+section of the Gerrit documentation tells you all you need to know about
+developer setup, CLAs, how to propose new features to the community etc.
+
+### Where do I start?
+
+If you want to contribute to the Gerrit community, but don't know were to start,
+there is a set of well defined Bugs and Feature Requests of various sizes
+in the [Help Wanted hotlist](https://issues.gerritcodereview.com/hotlists/5395287)
+in the issue-tracker.
+Just pick any of these issues that seem interesting, assign it to yourself and
+start.
+
+If you want you can present yourself to the community and announce that you
+have started working on the issue in any of the [community forums](contact.html).
+This will provide some context for the community if (when) you have additional
+questions or issues.