Update install.xhp to say to use composer

Closes #471

__docs/phpdoc/doc-base/entities/global.ent

@@ -657,7 +657,7 @@
 <!ENTITY url.xchm "http://xchm.sourceforge.net/">
 <!ENTITY url.xdebug "http://xdebug.org/">
 <!ENTITY url.xdiff "http://www.xmailserver.org/xdiff-lib.html">
-<!ENTITY url.xhp "https://github.com/facebook/xhp/tree/master/php-lib">
+<!ENTITY url.xhp "https://github.com/facebook/xhp">
 <!ENTITY url.xhprof.docs.facebook "http://web.archive.org/web/20110514095512/http://mirror.facebook.net/facebook/xhprof/doc.html">
 <!ENTITY url.xhprof.gui.fork1 "http://github.com/preinheimer/xhprof">
 <!ENTITY url.xinclude.spec "http://www.w3.org/TR/xinclude/">

__docs/phpdoc/en/install/xhp.xml

@@ -17,14 +17,16 @@ Fatal error: Class undefined: xhp_html in /
     you need to include the XHP library in your project.
   </para>
   <para>
-    You can find the XHP library in <link xlink:href="&url.xhp;">Github</link>. Put the files found here somewhere in your source tree.
+    You can find the XHP library in <link xlink:href="&url.xhp;">Github</link>. Add the following lines to your <literal>composer.json</literal> to install the library.
+   <programlisting>
+   "require": {
+     "facebook/xhp-lib": "dev-master"
+   }
+   </programlisting>
   </para>
   <para>
     Finally, either (1) change the XHP files from <literal>&lt;?php</literal> to <literal>&lt;?hh // decl</literal> (since XHP class name is supported out of the box in Hack) or (2) set <literal>hhvm.eval.enable_xhp=true</literal> in your <literal>.ini</literal> file or directly on the command line when running HHVM.
   </para>
-  <para>
-    Finally <literal>include init.php;</literal> before you use any XHP functionality.
-  </para>
 </chapter>
 
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