Add the WIP 10k ref architecture specs to HA docs

The 10,000 user reference architecture work is ongoing. However, we have
done some preliminary investigation and testing and have an idea of
what we think the environment might look like. In the interest of
transparency, efficiency and iteration, let's get this out there.

doc/administration/high_availability/README.md

@@ -145,14 +145,38 @@ environments this is a good architecture to consider if you foresee or do have
 contention due to certain workloads.
 
 - 3 PostgreSQL nodes
+- 1 PgBouncer node
 - 2 Redis nodes
 - 3 Consul/Sentinel nodes
 - 2 or more Sidekiq nodes
-- 2 or more Web nodes (Unicorn, Workhorse, PGBouncer)
+- 2 or more GitLab application nodes (Unicorn, Workhorse)
 - 1 or more NFS/Gitaly servers
+- 1 Monitoring node (Prometheus, Grafana)
 
 ![Hybrid architecture diagram](https://docs.gitlab.com/ee/administration/img/high_availability/hybrid.png)
 
+#### Reference Architecture
+
+- **Status:** Work-in-progress
+- **Supported Users (approximate):** 10,000
+- **Related Issues:** [gitlab-com/support/support-team-meta#1513](https://gitlab.com/gitlab-com/support/support-team-meta/issues/1513), 
+ [gitlab-org/quality/team-tasks#110](https://gitlab.com/gitlab-org/quality/team-tasks/issues/110)
+
+The Support and Quality teams are in the process of building and performance testing
+an environment that will support about 10,000 users. The specifications below
+are a work-in-progress representation of the work so far. Quality will be 
+certifying this environment in FY20-Q2. The specifications may be adjusted 
+prior to certification based on performance testing. 
+
+- 3 PostgreSQL - 4 CPU, 8GB RAM
+- 1 PgBouncer - 2 CPU, 4GB RAM
+- 2 Redis - 2 CPU, 8GB RAM
+- 3 Consul/Sentinel - 2 CPU, 2GB
+- 4 Sidekiq - 4 CPU, 8GB RAM
+- 5 GitLab application nodes - 20 CPU, 64GB RAM
+- 1 Gitaly - 20 CPU, 64GB RAM
+- 1 Monitoring node - 4 CPU, 8GB RAM
+
 ### Fully Distributed
 
 This architecture scales to hundreds of thousands of users and projects and is