Merge "Reload latest SHA1 from local when filtering RemoteRefUpdate" into stable-3.4
diff --git a/README.md b/README.md
index 79094d3..dcae980 100644
--- a/README.md
+++ b/README.md
@@ -65,6 +65,21 @@
daemon running (/var/run/docker.sock accessible) or a DOCKER_HOST pointing to
a Docker server.
+## Pre-requisites
+
+Each Gerrit server of the cluster must be identified with a globally unique
+[instance-id](https://gerrit-documentation.storage.googleapis.com/Documentation/3.4.5/config-gerrit.html#gerrit.instanceId)
+defined in `$GERRIT_SITE/etc/gerrit.config`.
+When migrating from a multi-site configuration with Gerrit v3.3 or earlier,
+you must reuse the instance-id value stored under `$GERRIT_SITE/data/multi-site`.
+
+Example:
+
+```
+[gerrit]
+ instanceId = 758fe5b7-1869-46e6-942a-3ae0ae7e3bd2
+```
+
## How to configure
Install the multi-site plugin into the `$GERRIT_SITE/lib` directory of all
