docs and typos

docs/media_keys.md

@@ -1,6 +1,6 @@
 # Media Keys
-Media keys extention adds keys for common media control keys. It can simply be 
-added to the extentions list.
+Media keys extension adds keys for common media control keys. It can simply be 
+added to the extensions list.
 
 ```python
 from kmk.extensions.media_keys import MediaKeys