Docs: Link single-node restart note to Puma explanation

doc/administration/reference_architectures/index.md

@@ -115,7 +115,8 @@ to the default installation:
 > - Supported tiers: [GitLab Starter, Premium, and Ultimate](https://about.gitlab.com/pricing/)
 
 GitLab supports [zero-downtime updates](https://docs.gitlab.com/omnibus/update/#zero-downtime-updates).
-Although you can perform zero-downtime updates with a single GitLab node, the recommendation is to separate GitLab into several application nodes.
+Single GitLab nodes can be updated with only a [few minutes of downtime](https://docs.gitlab.com/omnibus/update/README.html#single-node-deployment).
+To avoid this, we recommend to separate GitLab into several application nodes.
 As long as at least one of each component is online and capable of handling the instance's usage load, your team's productivity will not be interrupted during the update.
 
 ### Automated database failover **(PREMIUM ONLY)**

doc/update/README.md

@@ -50,7 +50,8 @@ However, for this to work there are the following requirements:
    migrations](../development/post_deployment_migrations.md) (included in
    zero downtime update steps below).
 - You are using PostgreSQL. Starting from GitLab 12.1, MySQL is not supported.
-- Multi-node GitLab instance. Single-node instances may experience brief interruptions as services restart.
+- Multi-node GitLab instance. Single-node instances may experience brief interruptions
+  [as services restart (Puma in particular)](https://docs.gitlab.com/omnibus/update/README.html#single-node-deployment).
 
 Most of the time you can safely upgrade from a patch release to the next minor
 release if the patch release is not the latest. For example, upgrading from