update documentation

update documentation to refer to the correct parameter: HIDE_DOCS

Author: rhoog

README.md

@@ -58,7 +58,7 @@ Finally include the `rest_framework_docs` urls in your `urls.py`:
 You can find detailed information about the package's settings at [the docs](http://drfdocs.com/docs/settings/).
 
     REST_FRAMEWORK_DOCS = {
-        'HIDDEN': True  # Default: False
+        'HIDE_DOCS': True  # Default: False
     }