Add docs and enable cookiecutter to support other templates

tools/cookiecutter/Dockerfile

@@ -1,5 +1,3 @@
 FROM python:3.8-slim
-
 RUN pip install cookiecutter==1.7.0 --index-url https://pypi.python.org/simple
-
 ENTRYPOINT [ "cookiecutter" ]

tools/cookiecutter/init.sh

@@ -0,0 +1,10 @@
+#!/usr/bin/env bash
+
+set -e
+
+# Build the container
+docker build $(pwd)/tools/cookiecutter -t backstage/tools/cookiecutter --quiet
+
+# Run cookiecutter with our arguments
+COOKIECUTTER_FLAGS=${@:-""}
+docker run -it -v $(pwd):/app -w /app backstage/tools/cookiecutter $COOKIECUTTER_FLAGS