docs(meta): Add dev instructions

README.md

@@ -57,3 +57,176 @@ The end result is a directory structure that has everything you need to hit the
     └── env
         └── fully.qualified.domain.name.example
 ```
+
+# Developing
+
+To change Cookiecutter templates get yourself an environment then make, test and commit your changes. First things first, the environment.
+
+## Environment
+
+Get yourself a Python virtual environment. In this example we're assuming you're running a Linux operating system and you'll be using [pyenv](https://github.com/pyenv/pyenv) to manage virtual environments.
+
+### pyenv
+
+- Install pyenv with what they are calling their automatic installer. Feel free to also read up on pyenv on their [GitHub project page](https://github.com/pyenv/pyenv).
+    ```
+    curl https://pyenv.run | bash
+    ```
+
+- Following the installer's instruction add at least the following commands to your `~/.bashrc` file
+    ```
+    export PYENV_ROOT="$HOME/.pyenv"
+    command -v pyenv >/dev/null || export PATH="$PYENV_ROOT/bin:$PATH"
+    eval "$(pyenv init -)"
+    ```
+
+- You will also likely want to add this line which will make sure pyenv auto-activates venvs when you navigate into certain directories. More on that down at [venv](#venv).
+    ```
+    eval "$(pyenv virtualenv-init -)"
+    ```
+
+- Also make sure `~/.bashrc` gets loaded for example by including this in a `~/.bash_profile` file
+    ```
+    [[ -f ~/.bashrc ]] && . ~/.bashrc
+    ```
+
+- Reload `~/.bashrc`
+    ```
+    source ~/.bashrc
+    ```
+
+### Python
+
+- Update pyenv's package list
+    ```
+    pyenv update
+    ```
+- Pick a Python version you like, for example copy-paste `3.11.4`:
+    ```
+    pyenv install --list | less
+
+    ...
+    3.10.12
+    3.11.0
+    3.11-dev
+    3.11.1
+    3.11.2
+    3.11.3
+    3.11.4
+    3.12.0b2
+    3.12-dev
+    3.13-dev
+    ...
+    ```
+- Install Python, wait for compilation to finish on your machine
+    ```
+    pyenv install 3.11.4
+    ```
+
+### Repo
+
+- Clone this repo
+    ```
+    git clone https://quico.space/Quico/py-cookiecutter-templates.git ~/py-cookiecutter-templates
+    ```
+
+### venv
+
+- Create a virtual environment where `3.11.4` is the Python version you want to use in this venv and `cookiecutter-3.11.4` is the name of your venv. Adding or dropping the Python version from your venv name comes down to personal preference.
+    ```
+    pyenv virtualenv 3.11.4 cookiecutter-3.11.4
+    ```
+
+- In your repo path `~/py-cookiecutter-templates` create a `.python-version` file to tell pyenv to always activate your desired venv when inside this dir.
+    ```
+    cd ~/py-cookiecutter-templates
+    pyenv local cookiecutter-3.11.4
+    ```
+    pyenv will immediately prefix your shell's `${PS1}` prompt with the venv name.
+    ```
+    (cookiecutter-3.11.4) [✔ 23:19 user@machine py-cookiecutter-templates]$ 
+    ```
+    It will deactivate the venv and drop its prefix as soon as you navigate out of this dir.
+    ```
+    (cookiecutter-3.11.4) [✔ 23:19 user@machine py-cookiecutter-templates]$ cd
+    [✔ 23:19 user@machine ~]$ 
+    ```
+    For now though stay in `~/py-cookiecutter-templates`, you're going to want to pip-install [cookiecutter](https://pypi.org/project/cookiecutter).
+
+- Upgrade `pip`
+    ```
+    pip install --upgrade pip
+    ```
+
+- Install [cookiecutter](https://pypi.org/project/cookiecutter)
+    ```
+    pip install cookiecutter
+    ```
+
+All done, your environment is set up.
+
+## Change
+
+Make some code changes, for example to the Docker Compose Cookiecutter template. When you're happy run your local Cookiecutter template to see how your changes are rendering.
+
+- Create `/tmp/cookiecutter-docker-compose`
+    ```
+    mkdir '/tmp/cookiecutter-docker-compose'
+    ```
+
+- Render a Docker Compose directory into your output directory, answer Cookiecutter's prompts:
+    ```
+    # cookiecutter ~/py-cookiecutter-templates \
+        --directory docker-compose \
+        --output-dir /tmp/cookiecutter-docker-compose
+
+    project_slug [dir-name]: mydir
+    service [mydir]: myservice
+    component_list [myservice]: mycomponent_one,mycomponent_two
+    context [ctx]: ux_novosibirsk
+    ```
+
+- Observe that in `/tmp/cookiecutter-docker-compose` you now have your rendered Docker Compose dir:
+    ```
+    # tree /tmp/cookiecutter-docker-compose
+
+    /tmp/cookiecutter-docker-compose
+    └── mydir
+        ├── build-context
+        │   ├── mycomponent_one
+        │   │   ├── docker-data
+        │   │   ├── Dockerfile
+        │   │   └── extras
+        │   └── mycomponent_two
+        │       ├── docker-data
+        │       ├── Dockerfile
+        │       └── extras
+        ├── common-settings.yml
+        ├── docker-compose.override.yml
+        ├── docker-compose.yml
+        └── env
+            └── fqdn_context.env.example
+    ```
+
+- For rapid testing you will most likely want to not type prompt answers repeatedly. Give them as command line arguments instead, also specify `--no-input` to suppress prompts:
+    ```
+    cookiecutter ~/py-cookiecutter-templates \
+        --no-input \
+        --directory docker-compose \
+        --output-dir /tmp/cookiecutter-docker-compose \
+        project_slug=mydir \
+        service=myservice \
+        component_list=mycomponent_one,mycomponent_two \
+        context=ux_novosibirsk
+    ```
+
+## Commit prep
+
+When you're about ready to commit changes into this repo check the following bullet points.
+
+- Did you update the [Cookiecutter template README.md file](docker-compose/README.md), here for example for Docker Compose?
+    - Change in behavior?
+    - An updated example directory layout?
+    - Updated example file content?
+- Did you commit a new completely rendered example directory structure into [docker-compose/examples](docker-compose/examples) dir?
+- Did you change something that affects existing example directories? If so rerender them.