Updated local nox instructions

.github/CONTRIBUTING.md

@@ -5,9 +5,19 @@ description of best practices for developing scientific packages.
 
 # Quick development
 
-The fastest way to start with development is to use `nox``. This will set up a
-virtual environment for you to run all the checks and tests. `nox`` is pre-installed
-in the Codespaces environment.
+The fastest way to start with development is to use `nox`. This will set up a
+virtual environment for you to run all the checks and tests. There are 2 ways to
+install `nox`:
+
+## Codespaces
+
+Nox is pre-installed in the Codespaces environment. So, after activating a Codespace,
+you can just open the terminal and run `nox` to run all the checks and tests.
+
+## Local
+If you don't have nox, you can use `pipx run nox` to run it without installing, or `pipx install nox`. If you don't have `pipx` (`pip` for applications), then you can install with with `pip install pipx` (the only case were installing an application with regular pip is reasonable). If you use macOS, then `pipx` and `nox` are both in brew, use `brew install pipx nox`.
+
+## Nox basics
 
 To use, run `nox`. This will lint and test using every installed version of
 Python on your system, skipping ones that are not installed. You can also run
@@ -19,7 +29,7 @@ $ nox -s tests  # Python tests
 $ nox -s build  # Make an SDist and wheel
 ```
 
-Nox handles everything for you, including setting up an temporary virtual
+Nox handles everything for you, including setting up a temporary virtual
 environment for each run.
 
 # Setting up a development environment manually