Update dependency proxy docs with permissions note

doc/user/packages/dependency_proxy/index.md

@@ -89,6 +89,10 @@ You can authenticate using:
 - A [personal access token](../../../user/profile/personal_access_tokens.md) with the scope set to `read_registry` and `write_registry`.
 - A [group deploy token](../../../user/project/deploy_tokens/index.md#group-deploy-token) with the scope set to `read_registry` and `write_registry`.
 
+Users accessing the Dependency Proxy with a personal access token or username and password require
+at least [Guest membership](../../permissions.md#group-members-permissions)
+to the group they pull images from.
+
 #### SAML SSO
 
 When [SSO enforcement](../../group/saml_sso/index.md#sso-enforcement)