doc: add the download statistics badge

Author: BoboTiG

CHANGELOG

@@ -4,6 +4,7 @@ History:
 
 3.3.1   2018/xx/xx
       - Linux: fix a memory leak introduced with 7e8ae5703f0669f40532c2be917df4328bc3985e (fixes #72)
+      - doc: add the download statistics badge
 
 3.3.0   2018/09/04
       - Linux: add an error handler for the XServer to prevent interpreter crash (fix #61)

README.rst

@@ -1,10 +1,12 @@
 Python MSS
 ==========
 
+.. image:: https://travis-ci.org/BoboTiG/python-mss.svg?branch=master
+    :target: https://travis-ci.org/BoboTiG/python-mss
 .. image:: https://img.shields.io/badge/say-thanks-ff69b4.svg
     :target: https://saythanks.io/to/BoboTiG
-.. image:: https://travis-ci.org/BoboTiG/python-mss.svg?branch=dev
-    :target: https://travis-ci.org/BoboTiG/python-mss
+.. image:: https://pepy.tech/badge/mss
+    :target: https://pepy.tech/project/mss
 
 
 .. code-block:: python