fix typos in contributing doc

Author: asonnenschein

CONTRIBUTING.md

@@ -141,15 +141,15 @@ These commands can be performed on the entire repository, when run from the repo
 and
 
 ```console
-    $ yapf --diff -r .
+    $ yapf --in-place -r .
 ```
 The configuration for YAPF is given in `setup.cfg` and `.yapfignore`.
 See the YAPF link above for advanced usage.
 
 ##### Alternative to YAPF
 
 YAPF is not required to follow the style and formatting guidelines. You can
-perform all formatting on your own using the linting output as a guild. Painful,
+perform all formatting on your own using the linting output as a guide. Painful,
 maybe, but possible!
 
 ## Testing