docs: added information on rolling alpine tokens

packaging/alpine/README.md

@@ -0,0 +1,19 @@
+To generate new release keys, first start the alpine docker container:
+
+```bash
+docker run -it --rm -v $(pwd):/work/mise ghcr.io/jdx/mise:alpine
+```
+
+And inside the container:
+
+```bash
+sudo su - packager
+abuild-keygen -a -n
+```
+
+Then store them in Github secrets as `ALPINE_PRIV_KEY` and `ALPINE_PUB_KEY`.
+Note the name of the private key file, it will be something like `-5f2b2c4e.rsa`.
+Save that string as `ALPINE_KEY_ID` as another secret.
+
+Also, the `ALPINE_GITLAB_TOKEN` needs to be rolled as well, use the [alpine gitlab portal](https://gitlab.alpinelinux.org/-/user_settings/personal_access_tokens)
+to generate a new token and store it in Github secrets as `ALPINE_GITLAB_TOKEN`.