Merge pull request #151 from yrro/debug-metrics-explainer

Provide a message explaining that metrics are disabled when running i…

prometheus_flask_exporter/__init__.py

@@ -263,12 +263,17 @@ def register_endpoint(self, path, app=None):
             (by default it is the application registered with this class)
         """
 
-        if is_running_from_reloader() and not os.environ.get('DEBUG_METRICS'):
-            return
-
         if app is None:
             app = self.app or current_app
 
+        if is_running_from_reloader() and not os.environ.get('DEBUG_METRICS'):
+            app.logger.debug(
+                'Metrics are disabled when run in the Flask development server'
+                ' with reload enabled. Set the environment variable'
+                ' DEBUG_METRICS=1 to enable them anyway.'
+            )
+            return
+
         @self.do_not_track()
         def prometheus_metrics():
             accept_header = request.headers.get("Accept")