fix(docs): use 'reader' relation in perform-check example to match update-tuples

The perform-check.mdx example was using relation 'can_view', but the
update-tuples page creates relation 'reader'. This brings the two
getting-started examples into sync and prevents the ValidationException.

Author: maxloge

docs/content/getting-started/perform-check.mdx

@@ -144,11 +144,11 @@ To obtain the [access token](https://auth0.com/docs/get-started/authentication-a
 
 ### 02. Calling Check API
 
-To check whether user `user:anne` has relationship `can_view` with object `document:Z`
+To check whether user `user:anne` has relationship `reader` with object `document:Z`
 
 <CheckRequestViewer
   user={'user:anne'}
-  relation={'can_view'}
+  relation={'reader'}
   object={'document:Z'}
   allowed={true}
   skipSetup={true}