src/buildstream/element.py: __use_remote_execution() reword desc

Element Plugins now require the use of virtual directories as such
they do not influence RE support. Reword for config hierarchy.
diff --git a/src/buildstream/element.py b/src/buildstream/element.py
index 7f80d08..ac16e31 100644
--- a/src/buildstream/element.py
+++ b/src/buildstream/element.py
@@ -2721,8 +2721,8 @@
 
     # __use_remote_execution():
     #
-    # Returns True if remote execution is configured and the element plugin
-    # supports it.
+    # Returns True if remote execution is configured, defaults to user defined
+    # project-specific overrides, project config, or global user config.
     #
     def __use_remote_execution(self):
         return bool(self.__remote_execution_specs)