Docs: Fix discussion group reference on contributing page

Link on contributing#contribute-to-the-code was referenced to source/index.
Now is linked to the community page.

Change-Id: I805b36a152c443db918b80b797a70bb53df866e1
Signed-off-by: Juan Pereira <juanmanuel.pereira1@gmail.com>
diff --git a/src/source/contributing.jd b/src/source/contributing.jd
index 5f1b62f..c5b1bbd 100644
--- a/src/source/contributing.jd
+++ b/src/source/contributing.jd
@@ -46,4 +46,4 @@
 and by learning about <code>git</code>, <code>repo</code>, and other tools using the links to the left. 
 You can also view the activity on all contributions on our
 <a href="https://android-review.googlesource.com/">Gerrit server</a>.
-If you need help along the way, you can join our <a href="/source/index.html">discussion groups</a>.</p>
+If you need help along the way, you can join our <a href="/source/community.html">discussion groups</a>.</p>