Document why the rageshake version is master

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

@@ -9,6 +9,8 @@ matrix_rageshake_docker_repo: "https://github.com/matrix-org/rageshake/"
 matrix_rageshake_docker_repo_version: "{{ 'master' if matrix_rageshake_version == 'master' else matrix_rageshake_version }}"
 matrix_rageshake_docker_src_files_path: "{{ matrix_base_data_path }}/Dockerfile"
 
+# There are no stable container image tags yet.
+# See: https://github.com/matrix-org/rageshake/issues/69
 matrix_rageshake_version: "master"
 matrix_rageshake_docker_image: "{{ matrix_rageshake_docker_image_name_prefix }}matrix-org/rageshake:{{ matrix_rageshake_version }}"
 matrix_rageshake_docker_image_name_prefix: "{{ 'localhost/' if matrix_rageshake_container_image_self_build else 'ghcr.io/' }}"