Fix typo in documentation/style-guide.rst (#1368)

documentation/style-guide.rst

@@ -132,7 +132,7 @@ explanation.
  designed to guide a user through a problem-field.
  Both tutorials and how-to guides are instructional rather than explanatory
  and should provide logical steps on how to complete a task. However,
- how-to guides make more assumptions about the user's knoweldge and
+ how-to guides make more assumptions about the user's knowledge and
  focus on the user finding the best way to solve their own
  particular problem.