Update README.rst

Fix the `circup install ...` instruction.
Tested with `circup` to a PyPortal.

Author: lesamouraipourpre

README.rst

@@ -75,7 +75,7 @@ following command to install:
 
 .. code-block:: shell
 
-    circup install macropad
+    circup install adafruit_macropad
 
 Or the following command to update an existing version: