Add instruction on contributing a formulary function to the main README

README.md

@@ -2,6 +2,15 @@
 
 [![Documentation Status](https://readthedocs.org/projects/plasmapy-summer-school/badge/?version=latest)](https://plasmapy-summer-school.readthedocs.io/en/latest/?badge=latest)
 
+## Contents
+
+- [Example Notebooks](#example-notebooks)
+- [Tips](#tips)
+  - [Running tests](#running-tests)
+  - [Building documentation](#building-documentation)
+  - [`git` and GitHub](#git-and-github)
+  - [Contributing to the Formulary](#contributing-to-the-formulary)
+
 ## Example notebooks
 
 Here are links to use the notebooks.
@@ -10,7 +19,6 @@ Here are links to use the notebooks.
  - [PlasmaPy Particles and Formulary](https://colab.research.google.com/github/PlasmaPy/plasmapy-summer-school/blob/main/notebooks/particles-formulary.ipynb)
  - [New notebook](https://colab.research.google.com/github/PlasmaPy/plasmapy-summer-school/blob/main/notebooks/particles-formulary.ipynb)
 
-
 ## Tips
 
 ### Running tests
@@ -28,3 +36,40 @@ Build documentation locally at:
 ```bash
 nox -s docs
 ```
+
+### `git` and GitHub
+
+Simplified cartoon of the `git` and GitHub scheme.
+
+![Cartoon of git and GitHub](./docs/source/_static/images/cartoon_local_git_and_github.png)
+
+### Contributing to the Formulary
+
+At this point we assume you have already forked this repository and set
+up  your local `git` repository.
+
+1. Start by determining which formulary function you would like to add
+   to the repo.  You can select from existing formulary functions
+   contained in the [`plasmapy.formulary`](https://github.com/PlasmaPy/PlasmaPy/tree/main/src/plasmapy/formulary)
+   or choose one of your own.
+2. Back at your local `git` clone (on your personal computer) update the
+   `main` branch.  This is the local branch that has its upstream set
+   the `main` branch of the [`plasmapy-summer-school` repository](https://github.com/PlasmaPy/plasmapy-summer-school).
+   This will ensure you are starting from the most up-to-date version
+   of the repository.
+3. Create a working branch from your updated `main` branch.  Name this
+   working branch something explicitly descibing what you are adding.
+   For example, name the working branch `add_gyroradius` for contributing
+   a formulary function for the gyroradius.
+4. Push an instance of your working branch to your GitHub fork of
+   `plasmapy-summer-school`.
+5. Now, add the code associated with your formulary function to the
+   appropriate `.py` file located in the `./src/hack/formulary` directory.
+   - As you develop your code try to make frequent, well focused commits.
+     This is not a strict rule, but will help with debugging errors if,
+     and when, they occur.
+6. Push you commits to GitHub at a regular intervals.
+7. When ready, open a Pull Request (PR) from your working branch on your
+   fork to the `main` branch on the original repository.  For detailed
+   instructions follow GitHub's instructions of
+   [Creating a pull request from a fork](https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/creating-a-pull-request-from-a-fork).