Cleaning up source.android.com files.

This change fixes some formatting artifacts that resulted from the export from
Sites, and also updates links to no longer point to Sites and use the standard
{@docRoot} idiom. Also contains a few content updates, and introduces a page
about branch management.
diff --git a/pdk/docs/source/overview.jd b/pdk/docs/source/overview.jd
index 0948ef2..9874b4b 100644
--- a/pdk/docs/source/overview.jd
+++ b/pdk/docs/source/overview.jd
@@ -3,9 +3,9 @@
 @jd:body
 <p>This page provides a high-level overview of the new features added to
 Android 1.6. To see the code itself, you can either use the <a
-href="http://git.source.android.com/">GitWeb</a>
+href="http://android.git.kernel.org/">GitWeb</a>
 interface to view snapshots of the files, or you can <a
-href="http://source.android.com/download/idex.html">download</a>
+href="{@docRoot}source/download.html">download</a>
 the source code onto your local machine. You can use <code>repo init -u
 git://android.git.kernel.org/platform/manifest.git -b android-1.6</code>
 to download the source code for Android 1.6.</p>