Update README.rst

Corrected typo.

Author: cameronsocialhardware

README.rst

@@ -11,7 +11,7 @@ Open Sound Control server and client implementations in **pure python** (3.5+).
 Current status
 ==============
 
-This library was developped following the specifications at
+This library was developed following the specifications at
 http://opensoundcontrol.org/spec-1_0
 and is currently in a stable state.