Update comments for `matrix_*_container_image_customizations_dockerfile_body_custom` variables to mention `matrix_*_container_image_customizations_enabled`

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/4011

roles/custom/matrix-bot-maubot/defaults/main.yml

@@ -120,6 +120,8 @@ matrix_bot_maubot_container_image_customizations_enabled: false
 # for building your customized maubot image based on the original (upstream) image (`matrix_bot_maubot_docker_image`).
 # A `FROM …` clause is included automatically so you don't have to.
 #
+# For this to take effect, you need to enable customizations (`matrix_bot_maubot_container_image_customizations_enabled: true`).
+#
 # Example:
 # matrix_bot_maubot_container_image_customizations_dockerfile_body_custom: |
 #  RUN echo 'This is a custom step for building the customized container image for maubot.'

roles/custom/matrix-synapse/defaults/main.yml

@@ -84,6 +84,8 @@ matrix_synapse_container_image_customizations_templates_git_repository_keyscan_h
 # for building your customized Synapse image based on the original (upstream) image (`matrix_synapse_docker_image`).
 # A `FROM …` clause is included automatically so you don't have to.
 #
+# For this to take effect, you need to enable customizations (`matrix_synapse_container_image_customizations_enabled: true`).
+#
 # Example:
 # matrix_synapse_container_image_customizations_dockerfile_body_custom: |
 #  RUN echo 'This is a custom step for building the customized Docker image for Synapse.'