Docker support (#99)

* add Dockerfile

* add basic documentation for docker image

* change cmd to entrypoint in Dockerfile

This is so that you can add args without docker assuming you're trying
to override the command

* Create docker-publish.yml github CI action

This is taken from the marketplace, I didn't write this

* correct docker image tag

* fix checkpoint loading (use carry for add)

* Fix digit typos in README

* revamp docker support

don't use volume, use latest alpine so i won't need to bump it
use multistage static build for minimal size with stripping
correctly save git version details

* tweak workflows

* try making cosign work

* Revert "try making cosign work"

This reverts commit a70723db66.

* fix

* remove root dockerfile

---------

Co-authored-by: cathugger <cathugger@cock.li>
Co-authored-by: dunsany <118174187+dunsany@users.noreply.github.com>

README.md

@@ -103,6 +103,15 @@ performance-related tips.
   It appears that onionbalance supports loading usual
   `hs_ed25519_secret_key` key so it should work.
 
+* Is there a docker image?
+
+  Yes, if you do not wish to compile mkp224o yourself, you can use
+  the `ghcr.io/cathugger/mkp224o` image like so:
+
+  ```bash
+  docker run --rm -it -v $PWD:/keys ghcr.io/cathugger/mkp224o:master -d /keys neko
+  ```
+
 ### Acknowledgements & Legal
 
 To the extent possible under law, the author(s) have dedicated all