Update contributing guide (#4274)

CONTRIBUTING.md

@@ -2,41 +2,81 @@
 
 Always happy to get issues identified and pull requests!
 
-## Getting your pull request merged in
+## General considerations
 
-1.  Keep it small. The smaller the pull request, the more likely we are to accept.
+1. Keep it small. The smaller the change, the more likely we are to accept.
-2.  Pull requests that fix a current issue get priority for review.
+2. Changes that fix a current issue get priority for review.
+3. Check out [GitHub guide][submit-a-pr] if you've never created a pull request before.
+
+## Getting started
+
+1. Fork the repo
+2. Clone your fork
+3. Create a branch for your changes
+
+This last step is very important, don't start developing from master, it'll cause pain if you need to send another change later.
 
 ## Testing
 
+You'll need to run the tests using Python 3.11. We recommend using [tox](https://tox.readthedocs.io/en/latest/) to run the tests. It will automatically create a fresh virtual environment and install our test dependencies, such as [pytest-cookies](https://pypi.python.org/pypi/pytest-cookies/) and [flake8](https://pypi.python.org/pypi/flake8/).
+
+We'll also run the tests on GitHub actions when you send your pull request, but it's a good idea to run them locally before you send it.
+
 ### Installation
 
-Please install [tox](https://tox.readthedocs.io/en/latest/), which is a generic virtualenv management and test command line tool.
+First, make sure that your version of Python is 3.11:
 
-[tox](https://tox.readthedocs.io/en/latest/) is available for download from [PyPI](https://pypi.python.org/pypi) via [pip](https://pypi.python.org/pypi/pip/):
+```bash
+$ python --version
+Python 3.11.3
+```
 
-    $ pip install tox
+Any version that starts with 3.11 will do. If you need to install it, you can get it from [python.org](https://www.python.org/downloads/).
 
-It will automatically create a fresh virtual environment and install our test dependencies,
+Then install `tox`, if not already installed:
-such as [pytest-cookies](https://pypi.python.org/pypi/pytest-cookies/) and [flake8](https://pypi.python.org/pypi/flake8/).
 
-### Run the Tests
+```bash
+$ python -m pip install tox
+```
 
-Tox uses pytest under the hood, hence it supports the same syntax for selecting tests.
+### Run the template's test suite
 
-For further information please consult the [pytest usage docs](https://pytest.org/latest/usage.html#specifying-tests-selecting-tests).
+To run the tests of the template using the current Python version:
 
-To run all tests using various versions of python in virtualenvs defined in tox.ini, just run tox.:
+```bash
+$ tox -e py
+```
 
-    $ tox
+This uses `pytest `under the hood, and you can pass options to it after a `--`. So to run a particular test:
 
-It is possible to test with a specific version of python. To do this, the command
+```bash
-is:
+$ tox -e py -- -k test_default_configuration
+```
 
-    $ tox -e py311
+For further information, please consult the [pytest usage docs](https://pytest.org/en/latest/how-to/usage.html#specifying-which-tests-to-run).
 
-This will run pytest with the python3.11 interpreter, for example.
+### Run the generated project tests
 
-To run a particular test with tox for against your current Python version:
+The template tests are checking that the generated project is fully rendered and that it passes `flake8`. We also have some test scripts which generate a specific project combination, install the dependencies, run the tests of the generated project, install FE dependencies and generate the docs. They will install the template dependencies, so make sure you create and activate a virtual environment first.
 
-    $ tox -e py -- -k test_default_configuration
+```bash
+$ python -m venv venv
+$ source venv/bin/activate
+```
+
+These tests are slower and can be run with or without Docker:
+
+- Without Docker: `scripts/test_bare.sh` (for bare metal)
+- With Docker: `scripts/test_docker.sh`
+
+All arguments to these scripts will be passed to the `cookiecutter` CLI, letting you set options, for example:
+
+```bash
+$ scripts/test_bare.sh use_celery=y
+```
+
+## Submitting a pull request
+
+Once you're happy with your changes and they look ok locally, push and send send [a pull request][submit-a-pr] to the main repo, which will trigger the tests on GitHub actions. If they fail, try to fix them. A maintainer should take a look at your change and give you feedback or merge it.
+
+[submit-a-pr]: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/creating-a-pull-request