adding disable mailnews and composer to the recommended .mozconfig file

browser/README.html

@@ -139,6 +139,8 @@
         ac_add_options --enable-crypto<br>
         ac_add_options --disable-tests<br>
         ac_add_options --disable-debug<br>
+        ac_add_options --disable-mailnews<br>
+        ac_add_options --disable-composer<br>
         ac_add_options --enable-optimize=-O2<br>
         <br>
        </code>