Docs: add python-networkx dependency to build documentation

Bug: 21922097
Change-Id: Ifd636ac579ba499a3f500dff6e85b3c287d963c2
diff --git a/src/source/initializing.jd b/src/source/initializing.jd
index 7d9e000..6c52343 100644
--- a/src/source/initializing.jd
+++ b/src/source/initializing.jd
@@ -79,7 +79,7 @@
 
 <h3 id="installing-required-packages-ubuntu-1404">Installing required packages (Ubuntu 14.04)</h3>
 <p>You will need a 64-bit version of Ubuntu. Ubuntu 14.04 is recommended.</p>
-<pre><code>$ sudo apt-get install bison g++-multilib git gperf libxml2-utils make zlib1g-dev:i386 zip</code></pre>
+<pre><code>$ sudo apt-get install bison g++-multilib git gperf libxml2-utils make python-networkx zlib1g-dev:i386 zip</code></pre>
 
 <h3 id="installing-required-packages-ubuntu-1204">Installing required packages (Ubuntu 12.04)</h3>
 <p>You may use Ubuntu 12.04 to build older versions of Android. Version 12.04 is not supported on master or recent releases.</p>