Update README.rst

Adds mention of dropping python 2.7 support to the readme.

Author: allmightyspiff

README.rst

@@ -129,6 +129,13 @@ System Requirements
 * A connection to SoftLayer's private network is required to use
   our private network API endpoints.
 
+Pyhton 2.7 Support
+------------------
+As of version 5.8.0 SoftLayer-Python will no longer support python2.7, which is _`End Of Life as of 2020 <https://www.python.org/dev/peps/pep-0373/>`_. 
+If you cannot install python 3.6+ for some reason, you will need to use a version of softlayer-python <= 5.7.2
+
+
+
 Python Packages
 ---------------
 * ptable >= 0.9.2