Merge pull request percona#25 from percona/PMM-7087-clarifications

PMM-7087 clarifications

Author: PaulJacobs-percona

queries-postgres.yml

@@ -1,3 +1,7 @@
+## ######################################################
+## WARNING: This is an example. Do not edit this file. 
+## To create your own Custom Queries - create a new file
+## ######################################################
 ## Custom query example.
 #pg_replication:
 #  query: "SELECT EXTRACT(EPOCH FROM (now() - pg_last_xact_replay_timestamp())) as lag"