docs: add installation and publishing instructions for Gitea package registry

README.md

@@ -37,6 +37,38 @@ From outside the checkout, point `PYTHONPATH` at it:
 PYTHONPATH=/path/to/mailinabox python3 -m mailinabox.cli.miab --help
 ```
 
+### Install from the Gitea package registry
+
+```sh
+pip install --index-url https://<username>:<token>@<gitea-host>/api/packages/<owner>/pypi/simple mailinabox
+```
+
+> **Note** `python-helpers` is resolved from the same registry. If it is published elsewhere,
+> install it first and add `--no-deps` here.
+
+## Publishing
+
+Add the registry to `~/.pypirc`:
+
+```
+[distutils]
+index-servers = gitea
+
+[gitea]
+repository = https://<gitea-host>/api/packages/<owner>/pypi
+username = <username>
+password = <token>
+```
+
+```sh
+pip install build twine
+python3 -m build
+python3 -m twine upload --repository gitea dist/*
+```
+
+> **Note** a name and version already in the registry cannot be republished. Raise `version`
+> in `pyproject.toml` before each upload.
+
 ## Library
 
 ```python