Update readme to include a supported versions

Author: crwilcox

packages/google-cloud-ndb/README.md

@@ -14,3 +14,30 @@ Learn how to use the `ndb` library by visiting the Google Cloud Platform
 [0]: https://cloud.google.com/datastore
 [1]: https://cloud.google.com/appengine
 [2]: https://cloud.google.com/appengine/docs/python/ndb/
+
+## Installation 
+
+Install this library in a virtualenv using pip. virtualenv is a tool to create isolated Python environments. The basic problem it addresses is one of dependencies and versions, and indirectly permissions.
+
+With virtualenv, it's possible to install this library without needing system install permissions, and without clashing with the installed system dependencies.
+
+### Supported Python Versions
+Python >= 3.6
+
+As this package is designed to work in the [AppEngine runtime](https://cloud.google.com/appengine/docs/python/) Python 3.6+ are supported. 
+
+### Mac/Linux
+```
+pip install virtualenv
+virtualenv <your-env>
+source <your-env>/bin/activate
+<your-env>/bin/pip install google-cloud-ndb
+```
+
+### Windows
+```
+pip install virtualenv
+virtualenv <your-env>
+<your-env>\Scripts\activate
+<your-env>\Scripts\pip.exe install google-cloud-ndb
+```