Update README.md for Python 3

Added information regarding Python 3 support.

Author: alperenkose

README.md

@@ -1,3 +1,7 @@
+Important Note
+===
+This is an updated version of geeknote for Python 3 using evernote-sdk-python3 (which is also in beta). Even though things are not throughly tested, basic functionality works.
+
 Geeknote for Evernote (or 印象笔记)  [![Travis CI](https://travis-ci.org/jeffkowalski/geeknote.svg?branch=master)](https://travis-ci.org/jeffkowalski/geeknote) [![Circle CI](https://circleci.com/gh/jeffkowalski/geeknote.svg?&style=shield)](https://circleci.com/gh/jeffkowalski/geeknote)
 ===