Python 3.6 is required

We use some 3.6-specific features from the enum library, so older
versions won't work.

README.md

@@ -37,5 +37,5 @@ Interface
 
 ## Requirements
 
-* Python >= 3.4 should work (tested with 3.6)
+* Python >= 3.6
 * pySerial (tested with 3.3)