docs: Add CONTRIBUTING.md

CONTRIBUTING.md

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+# Contributing
+
+## Node Installation
+
+1. Install Node Version Manager (nvm) using the instructions [here][node]. Note: On Windows, it is
+   recommended to use "NVM for Windows". You can install this with Winget or Chocolatey.
+1. Install Node v21 using `nvm install 21`.
+1. Run `nvm use 21` to change your current version of node.
+
+[node]: https://github.com/nvm-sh/nvm#installing-and-updating
+
+## Yarn & Package Installation
+
+After Node is installed, you must install Yarn. These instructions were taken from [here][yarn].
+
+1. Install yarn using the command `corepack enable`.
+1. Then run `yarn install` to install all dependencies.
+
+[yarn]: https://yarnpkg.com/getting-started/install
+
+## Update Distribution
+
+The `dist` directory contains the published version of the github action. When a change is made, the
+distribution must be updated.
+
+1. Delete the current `dist` directory with `rm -rf dist`.
+1. Regenerate the distribution with `yarn build`.
+1. Commit all changes to the `dist` directory.