Clarify that external users can access public projects

doc/user/permissions.md

@@ -292,7 +292,7 @@ project and should only have access to that project.
 External users:
 
 - Cannot create groups, projects, or personal snippets.
-- Can only access projects to which they are explicitly granted access,
+- Can only access public projects and projects to which they are explicitly granted access,
   thus hiding all other internal or private ones from them (like being
   logged out).