Clarify monitoring backend provenance (influxdata#4739)

Author: jpmens

plugins/inputs/openldap/README.md

@@ -4,7 +4,7 @@ This plugin gathers metrics from OpenLDAP's cn=Monitor backend.
 
 ### Configuration:
 
-To use this plugin you must enable the [monitoring](https://www.openldap.org/devel/admin/monitoringslapd.html) backend.
+To use this plugin you must enable the [slapd monitoring](https://www.openldap.org/devel/admin/monitoringslapd.html) backend.
 
 ```toml
 [[inputs.openldap]]