README: Added the P-Star 25K50 Micro to the list of tested configurations.
README: Added the P-Star 25K50 Micro to the list of tested configurations.

Signed-off-by: David (Pololu) <f98e24a9f7404bdf2a357eeba39e935e143d3b2c@pololu.com>

pololu/m-stack,pololu/m-stack