Fix typo in demo README

Author: WasabiFan

demo/README.md

@@ -1,7 +1,7 @@
 # ev3dev demo programs
 
 This folder contains a bunch of demo programs that you can use to help you in
-developing your own code. Breif descriptions of each demo are provided below;
+developing your own code. Brief descriptions of each demo are provided below;
 you can access the full source code and some more detailed information on each
 by opening the respective folders above.