Fix spelling issue in documentation: approapriate -> appropriate

[charignon]

Summary

This PR fix spelling issues in documentation, the word "appropriate" was previously incorrectly spelled "approapriate".

Contribution checklist

• The commits are consistent with our [contribution guidelines][1]
• The new code is not generating bytecode or M-x checkdoc warnings
  • There is 12 warnings in the code on master, we should take a look, none introduced by this change
• You've updated the changelog (if adding/changing user-visible functionality)
  • I don't think we mentioned spelling fixes in the changelog before, so checking this one
• You've updated the readme (if adding/changing user-visible functionality)
  • Not necessary for this change (see answer above)