Update readme to call out change from Managed VMs to App Engine Flexible Environment (#79)

Update readme for managed vm -> flex change

Author: JustinBeckwith

README.md

@@ -1,16 +1,14 @@
-Google App Engine Managed VMs Python Compat Runtime
+Google App Engine Flexible Environment Python Compat Runtime
 ===================================================
 
-Warning
--------
-The instructions here are for a multi-process version of the Python 2.7 runtime
-**currently in alpha**. To use the stable version of the runtime, follow the
-documentation at https://cloud.google.com/appengine/docs/managed-vms/ instead.
+This repository contains the source code used for the [App Engine Flexible Environment](https://cloud.google.com/appengine/docs/flexible/) Python Compat runtime.  This runtime provides best effort compatibility with applications written to target the App Engine Standard Environment with Python 2.7. This runtime is currently in *alpha*.
+
+This runtime is intended for users migrating applications from App Engine Standard to App Engine Flex. For users building new applications on App Engine with Python, we recommend following the [getting started guide](https://cloud.google.com/python).  
+
 
 Using this runtime
 ------------------
-
-Please refer to [the docs](https://cloud.google.com/appengine/docs/managed-vms/python/migrating-an-existing-app) on how to use and customize this runtime.
+Please refer to [the docs](https://cloud.google.com/appengine/docs/flexible/python/migrating-an-existing-app) on how to use and customize this runtime.
 
 Gunicorn configuration
 ----------------------
@@ -24,7 +22,7 @@ application's root directory, which will override the default
 
 Caveats
 -------
-As this is a alpha product, some functionality has not yet been implemented.
+This runtime is currently an alpha.  As this is a alpha product, some functionality has not yet been implemented, and a few things may change.  
 
 Notably:
 * Handlers in `app.yaml `that are flagged as `login: required` or `login: admin` are not supported. Attemping to access these handlers will result in a 404 as the handlers will not be registered.