Make it clear which version of rocksdb is supported

docs/index.rst

@@ -10,7 +10,8 @@ Python bindings to the C++ interface of http://rocksdb.org/ using cython::
     db.put(b"a", b"b")
     print db.get(b"a")
 
-Tested with python2.7 and python3.3
+
+Tested with python2.7 and python3.3 and RocksDB version 2.7.fb
 
 .. toctree::
     :maxdepth: 2

docs/installation.rst

@@ -14,7 +14,7 @@ For more details consider https://github.com/facebook/rocksdb/blob/master/INSTAL
     $ git clone https://github.com/facebook/rocksdb.git
     $ cd rocksdb
     $ # It is tested with this version
-    $ git checkout ac2fe728327be75c8c289d4e3ebf8587d88c518d
+    $ git checkout 2.7.fb
     $ make librocksdb.so
 
 If you do not want to call ``make install`` export the following enviroment