Add contributing and update readme

CONTRIBUTING.md

@@ -0,0 +1,34 @@
+# Contributing
+
+Thank you for your interest in contributing to this project!
+
+This repository serves a dual purpose:
+1.  It is a [Copier](https://copier.readthedocs.io/) template.
+2.  It is a standard GitHub template repository.
+
+This is achieved through a CI/CD process where the `template` branch, containing the Copier Jinja2 templates, is rendered and pushed to the `main` branch. The `main` branch can then be used as a regular GitHub template.
+
+## Development Workflow
+
+Because of this setup, all development must happen on the `template` branch. The `main` branch is protected and automatically updated.
+
+To contribute, please follow these steps:
+
+1.  **Fork the repository.**
+2.  **Create a new branch from the `template` branch.**
+    ```bash
+    git checkout template
+    git checkout -b my-new-feature
+    ```
+3.  **Make your changes.**
+    -   Modify the template files. They have a `.jinja` extension if the content of the file is
+        manipulated, and the curly braces in the names is jinja too that is interpolated.
+    -   If you're adding new template variables, update `copier.yml`.
+4.  **Test your changes (if applicable).**
+    You can test the template rendering locally using `copier`.
+5.  **Commit your changes and push your branch.**
+6.  **Open a Pull Request against the `template` branch.**
+
+Your pull request will be reviewed, and once merged, a GitHub Actions workflow will automatically render the updated template and commit the result to the `main` branch.
+
+Direct pushes or pull requests to the `main` cannot be accepted.

README.md

@@ -19,6 +19,9 @@ It includes the following bits:
 - The rest of this README!
 
 ## 🤔 How to use this template
+This template can be used in two ways:
+
+### As a GitHub Template
 1. Hit the green `Use this template` button up on the right next to the stars
 2. Give your new repository a name and then clone it to your dev environment.
 3. Rename it:
@@ -28,6 +31,14 @@ It includes the following bits:
 4. Run `uv sync`
 5. Have a look at the stuff below here, try out some commands and edit this README as you like!
 
+### As a Copier Template
+Alternatively, you can use [Copier](https://copier.readthedocs.io/) to generate a new project from this template.
+This is the recommended approach as it allows you to configure the project with your details.
+
+```bash
+uxv copier copy -r template https://github.com/carderne/postmodern-python <my_project>
+```
+
 ## 💾 Installation (not development!)
 ```bash
 git clone git@github.com:carderne/postmodern-python.git

copier.yml

@@ -54,7 +54,7 @@ include_dockerfile:
   help: "Include a Dockerfile in the project?"
   default: yes
 
-_src_path: project_template
-_exlude:
+_exclude:
   - .venv/
   - .git/
+  - .github/workflows/render-template.yml