Add postgresql dsn connection string example (influxdata#5869)

Author: urusha

plugins/inputs/pgbouncer/README.md

@@ -5,7 +5,11 @@ This PgBouncer plugin provides metrics for your PgBouncer load balancer.
 More information about the meaning of these metrics can be found in the [PgBouncer Documentation](https://pgbouncer.github.io/usage.html)
 
 ## Configuration
-Specify address via a url matching:
+Specify address via a postgresql connection string:
+
+  `host=/run/postgresql port=6432 user=telegraf database=pgbouncer`
+
+Or via an url matching:
 
   `postgres://[pqgotest[:password]]@localhost[/dbname]?sslmode=[disable|verify-ca|verify-full]`
 

plugins/inputs/postgresql/README.md

@@ -31,7 +31,11 @@ _* value ignored and therefore not recorded._
 More information about the meaning of these metrics can be found in the [PostgreSQL Documentation](http://www.postgresql.org/docs/9.2/static/monitoring-stats.html#PG-STAT-DATABASE-VIEW)
 
 ## Configuration
-Specify address via a url matching:
+Specify address via a postgresql connection string:
+
+  `host=/run/postgresql user=telegraf database=telegraf`
+  
+Or via an url matching:
 
   `postgres://[pqgotest[:password]]@localhost[/dbname]?sslmode=[disable|verify-ca|verify-full]`