Crosslink prometheus and grafana to HA monitoring

doc/administration/high_availability/monitoring_node.md

@@ -4,7 +4,7 @@
 
 ## Standalone Monitoring node using GitLab Omnibus
 
-The GitLab Omnibus package can be used to configure a standalone Monitoring node running Prometheus and Grafana.
+The GitLab Omnibus package can be used to configure a standalone Monitoring node running [Prometheus](../monitoring/prometheus/index.md) and [Grafana](../monitoring/performance/grafana_configuration.md).
 The monitoring node is not highly available. See [Scaling and High Availability](README.md)
 for an overview of GitLab scaling and high availability options.