Update guide.md (#195)

fixed typo "customize of override" should be "customize or override"

Author: jimkring

docs/guide.md

@@ -297,7 +297,7 @@ You can then use `HasOrganizationAPIKey` as described in [Setting permissions](#
 
 By default, API key permission classes retrieve the API key from the `Authorization` header or a custom header, as described in [Making authorized requests](#making-authorized-requests).
 
-You can customize of override this behavior in several ways.
+You can customize or override this behavior in several ways.
 
 If you are building an API for an application you do not control that requires a specific header keyword, e.g. a client that sends API keys using the `Bearer` keyword as follows: