Add docs about DOCKER_CLI_EXPERIMENTAL=enabled

README.md

@@ -192,6 +192,10 @@ Check https://pulsar.apache.org for documentation and examples.
 
 ## Build custom docker images
 
+The commands used in the Apache Pulsar release process can be found in the [release process documentation](https://pulsar.apache.org/contribute/release-process/#stage-docker-images).
+
+Here are some general instructions for building custom docker images:
+
 * Docker images must be built with Java 8 for `branch-2.7` or previous branches because of [ISSUE-8445](https://github.com/apache/pulsar/issues/8445).
 * Java 11 is the recommended JDK version in `branch-2.8`, `branch-2.9` and `branch-2.10`.
 * Java 17 is the recommended JDK version in `master`.
@@ -200,6 +204,8 @@ The following command builds the docker images `apachepulsar/pulsar-all:latest`
 
 ```bash
 mvn clean install -DskipTests
+# setting DOCKER_CLI_EXPERIMENTAL=enabled is required in some environments with older docker versions
+export DOCKER_CLI_EXPERIMENTAL=enabled
 mvn package -Pdocker,-main -am -pl docker/pulsar-all -DskipTests
 ```