doc: clarify and separate in migration doc the two changes in 3.14 (sourcegraph#545)

* doc: clarify and separate in migration doc the two changes in 3.14

* Update docs/migrate.md

Co-Authored-By: Christina Forney <[email protected]>

* Update docs/migrate.md

Co-Authored-By: Christina Forney <[email protected]>

Co-authored-by: Christina Forney <[email protected]>

Author: uwedeportivo

docs/migrate.md

@@ -6,6 +6,8 @@ version you are upgrading to should be applied (unless otherwise noted).
 
 ## 3.14 (Unreleased)
 
+### Existing installations: Migrating the container user from root to non-root
+
 Version 3.14 changes the security context of the installation by switching to a non-root user for all containers.
 This allows running Sourcegraph in clusters with restrictive security policies.
 
@@ -37,6 +39,8 @@ restart the necessary containers.
 New installations do not need this `kustomization` and existing installations can operate from base again after the
 migration.
 
+### New installations: accommodate clusters with restrictive security policies
+
 New installations on clusters with restrictive security policies can now use a kustomization to accomodate those restrictions:
 
 ```shell script
@@ -135,4 +139,3 @@ Sourcegraph 3.0 ships with Postgres 11.1. The upgrade procedure is mostly automa
 ## 2.12
 
 Beginning in version 2.12.0, Sourcegraph's Kubernetes deployment [requires an Enterprise license key](https://about.sourcegraph.com/pricing). Follow the steps in [docs/configure.md](docs/configure.md#add-a-license-key).
-