Fix some of the more obvious typos

docs/getting_started_build_tools.md

@@ -118,7 +118,7 @@ If this is a bit complex for you, Docker might be the turn-key solution you need
 
 ```bash
 # You'll run this every time you want to build a keymap
-# modify the keymap and keyboard assigment to compile what you want
+# modify the keymap and keyboard assignment to compile what you want
 # defaults are ergodox/default
 
 docker run -e keymap=gwen -e keyboard=ergodox_ez --rm -v $('pwd'):/qmk:rw edasque/qmk_firmware