Fixes yaml code and example

Author: AArdeev

doc/code_snippets/snippets/config/instances.enabled/credentials/revoke.yaml

@@ -19,5 +19,5 @@
       password: '123456'
       roles: [ writers_space_reader ]
       privileges: []
-#      - permissions: [ read ]
+#      - permissions: [ read, write ]
 #        spaces: [ books ]

doc/platform/connections_and_auth/credentials.rst

@@ -90,7 +90,7 @@ previously allowed privilege, or with an empty ``privileges`` array. Further opt
 
 ..  literalinclude:: /code_snippets/snippets/config/instances.enabled/credentials/revoke.yaml
     :language: yaml
-    :start-at: sampleuser:
+    :start-at: # grant privileges
     :dedent:
 
 .. _configuration_credentials_loading_secrets: