Add Puffin Docker image (#985)
Missing piece for the release.
## Test Plan
Built the image locally:
```shell
❯ docker run 99956098e1f8f04e209dcfc4a0afcee67df1fe8a726c164884e67f035b1a0f42
Usage: puffin [OPTIONS] <COMMAND>
Commands:
pip Resolve and install Python packages
venv Create a virtual environment
clean Clear the cache
help Print this message or the help of the given subcommand(s)
Options:
-q, --quiet Do not print any output
-v, --verbose Use verbose output
-n, --no-cache Avoid reading from or writing to the cache
--cache-dir <CACHE_DIR> Path to the cache directory [env: PUFFIN_CACHE_DIR=]
-h, --help Print help
-V, --version Print version
```
