clear up dependency issues slightly

I encountered the problem from issue saltstack#391 with the latest develop in Ubuntu 12.04  and found it necessary to install ubuntu's packages for all the dependencies on the install page, then make sure to call virtualenv with --system-site-packages so pip did not try to compile those.

saltstack#391

HACKING.rst

@@ -54,7 +54,6 @@ Then::
 
 Installing Salt for development
 -------------------------------
-You need both ``swig`` and ``libssl-dev`` installed for Salt development.
 
 Clone the repository using::
 
@@ -64,6 +63,11 @@ Create a new `virtualenv`_::
 
     virtualenv /path/to/your/virtualenv
 
+.. note:: site packages
+
+    If you wish to use installed packages rather than have pip download and
+    compile new ones into this environment, add "--system-site-packages".
+
 .. _`virtualenv`: http://pypi.python.org/pypi/virtualenv
 
 Activate the virtualenv::
@@ -76,7 +80,8 @@ Install Salt (and dependencies) into the virtualenv::
 
 .. note:: Installing M2Crypto
 
-    If you and encounter the error ``command 'swig' failed with exit status 1``
+    You may need ``swig`` and ``libssl-dev`` to build M2Crypto. If you 
+    encounter the error ``command 'swig' failed with exit status 1``
     while installing M2Crypto, try installing it with the following command::
 
         env SWIG_FEATURES="-cpperraswarn -includeall -D__`uname -m`__ -I/usr/include/openssl" pip install M2Crypto