Fixes small typo in docs (#10515)

docs/hardware_keyboard_guidelines.md

@@ -192,7 +192,7 @@ When developing your keyboard, keep in mind that all warnings will be treated as
 
 ## Copyright Blurb
 
-If you're adapting your keyboard's setup from another project, but not using the same code, but sure to update the copyright header at the top of the files to show your name, in this format:
+If you're adapting your keyboard's setup from another project, but not using the same code, be sure to update the copyright header at the top of the files to show your name, in this format:
 
     Copyright 2017 Your Name <your@email.com>