Merge branch 'pc-add-graphs-quick-guide' into 'master'

Add quick guide for system graphs

See merge request !1

README.md

 # GitLab Infrastructure
 [These are not the runbooks you are looking for](https://gitlab.com/gitlab-com/runbooks)
+
+## Where and how to look for data
+
+### General System Health
+
+#### Blackbox Monitoring
+
+* [GitLab Web Status](http://performance.gitlab.net/dashboard/db/gitlab-web-status): front end perspective of GitLab. Useful to understand how GitLab.com looks from the user perspective. Use this graph to quickly troubleshoot what part of GitLab is slow.
+
+#### Whitebox Monitoring
+
+* [Fleet overview](http://performance.gitlab.net/dashboard/db/fleet-overview): useful to see the fleet status from the inside of GitLab.com. Use this graph to quickly see if the workers or the database are under heavy load, and to check load balancer bandwidth.
+
+* [Postgres Stats](http://performance.gitlab.net/dashboard/db/postgres-stats): useful to understand how is the database behaving in depth. Use this graph to review if we have spikes of exclusive locks, active or idle in transaction processes
+* [Ceph Stats](http://performance.gitlab.net/dashboard/db/ceph-stats): useful to understand the health of the underlying Rados cluster
+* [Host Stats](http://performance.gitlab.net/dashboard/db/host-stats): useful to dive deep into a specific host to understand what is going on with it. Select a host from the dropdown on the top.
+* [Postgres Queries](http://performance.gitlab.net/dashboard/db/postgres-queries) use this dashboard to understand if we have blocked or slow queries, dead tuples, etc.
+* [Business Stats](http://performance.gitlab.net/dashboard/db/business-stats): shows many pushes, new repos and CI builds.
+* [Daily overview](http://performance.gitlab.net/dashboard/db/daily-overview): shows endpoints with amount of calls and performance metrics. Useful to understand what is slow generally.