docs: add/update documentation (#38590)

docs/how-to-work-on-the-docs-theme.md

@@ -0,0 +1,43 @@
+# How to work on the docs theme
+
+> [!NOTE]
+> **You do not need to setup anything locally for working on the documentation content.**
+>
+> To work on the contributing guidelines, you can edit or add files in the `docs` directory [available here](https://github.com/freeCodeCamp/freeCodeCamp/tree/master/docs). When your changes are merged, it will be made available automatically at the documentation site.
+
+## About the documentation site
+
+While you do not need to generate the documenatation site locally, sometimes it may be required for instance if you are working on the site theme or a feature for the site.
+
+The site is generated using [`docsify`](https://docsify.js.org), and served using GitHub pages.
+
+Typically you would not need to change any configuration, or build the site locally, but incase you are interested here is how it works:
+
+- The homepage's source for this site is available in [`docs/index.html`](index.html).
+- We serve this file as a SPA using `docsify` and GitHub Pages.
+- The `docsify` script generates the content of `markdown` files in `docs` directory on demand.
+- The homepage is generated from the [`index.md`](index.md).
+- the sidebar navigation is generated from [`components/sidebar.md`](components/sidebar.md).
+
+## Serving the documenation site locally
+
+Clone freeCodeCamp:
+
+```sh
+git clone https://github.com/freeCodeCamp/freeCodeCamp.git
+docsify serve docs
+```
+
+Install `docsify`:
+
+```sh
+npm install -g docsify
+```
+
+and serve the `/docs` directory
+
+```sh
+docsify serve docs
+```
+
+Alternatively, if you have installed freeCodeCamp locally (see the local setup guide), we bundle the CLI with the development tools so you can run `npm run docs:serve` from the root of the repo.