Update RHEL build instructions

Author: arahlin

README.rst

@@ -52,14 +52,16 @@ If your system defaults to Python 2, but you wish to use Python 3, please do the
 
 On any system, this software requires numpy and scipy (hard requirements), plus astropy and healpy (optional).
 
-Setup on RHEL6
---------------
+Setup on RHEL Systems with OASIS
+--------------------------------
 
-Note that on any RHEL6 system, you will need a newer compiler than ships with the OS. Please follow whatever directions apply at your site to achieve this. Alternately, if you have OASIS set up on your local system, run this before anything else (also works on several other operating systems, including RHEL7):
+If using RHEL8 or RHEL9 and you have OASIS set up on your local system, run this before anything else:
 
 .. code-block:: shell
 
-	eval `/cvmfs/spt.opensciencegrid.org/py3-v4/setup.sh`
+	eval `/cvmfs/spt.opensciencegrid.org/py3-v5/setup.sh`
+
+This will add a relatively new compiler and all necessary development packages (FLAC, GSL, etc) for compiling this software.
 
 
 How to Build