chore: Port FreeSewing.dev to docusaurus

The replaces the NextJS site powering FreeSewing.dev with a Docusaurus
setup. It's part of my efforts to simplify FreeSewing's setup so we can
focus on our core value proposition.

sites/dev/docs/tutorials/getting-started-linux/dev-start/readme.mdx

@@ -0,0 +1,62 @@
+---
+title: Start the development environment
+order: 50
+---
+
+FreeSewing provides a development environment to help you design and develop patterns.
+
+There are two ways to run this development environment:
+
+- [**Monorepo development**](#monorepo-development): Use this if you intend to contribute your work to FreeSewing
+- [**Stand-alone development**](#stand-alone-development): Use this if you want to do your own thing, and not contribute to FreeSewing
+
+## Monorepo development
+
+Run `yarn lab` to start the development environment:
+
+```bash
+yarn lab
+```
+
+Then point your browser to http://localhost:8000
+
+:::tip
+### Adding a new design
+This is all you need to work on existing designs. If you'd like to add a new design, run:
+
+```bash
+yarn new design
+```
+
+Just make sure to re-start the lab afterwards with `yarn lab`
+:::
+
+## Stand-alone development
+
+You will have a new folder that has the name you picked for your design.
+If you chose `test`, you will have a folder named `test`.
+If you chose `banana`, you'll have a folder named `banana`.
+(Within this new folder, the `design` subfolder holds your design's configuration file and source code.
+You can ignore all other subfolders and files; they are part of the development environment.)
+
+To start the development environment, enter the folder that was created
+and run `yarn dev` (or `npm run dev` if you're using npm as a package manager).
+
+Then open your browser and go to http://localhost:8000
+
+:::tip
+The development environment will watch for any changes you make to
+the pattern's source code or configuration.
+When you do, it will update automatically in your browser.
+:::
+
+:::note
+
+##### Yay, you're done!
+
+All you have to do now is design your pattern.
+Thankfully, we have a tutorial for that too:
+
+- [Pattern design tutorial](/tutorials/pattern-design/): A step-by-step guide to designing your first pattern
+
+:::