Update CONTRIBUTING.md with development setup and code style guidelines

CONTRIBUTING.md

@@ -1,17 +1,35 @@
 # Contributing
 
-## Updating Game Assets
+This project is built in NodeJS, with [Svelte 5](https://svelte.dev/) and [SvelteKit](https://svelte.dev/docs/kit/introduction).
+
+## Development
+
+### Getting Started
+
+-   Clone the project
+-   Install the NodeJS version 20, 22, or later
+-   Run `npm install`
+
+### Local Development
+
+Run `npm run dev` to start the local dev server.
+
+### Updating Game Assets
 
 Follow [these](https://stardewvalleywiki.com/Modding:Editing_XNB_files#Unpack_game_files) instructions to unpack the game files. Put them in a `content` folder at the root of the project (eg. `content/Characters/Abigail.png`).
 
 Then run `npm run dump`.
 
 If you need assets that aren't copied from that command, you can modify it in `src/dump.ts`.
 
-## Reading the Save File
+### Reading the Save File
 
 The save format is somewhat inconsistent (in structure and consistency). My recommendation is to use a website like [this](https://jsonformatter.org/xml-parser) to format the save file into something more readable, then use a text editor to search for the data you need.
 
 ## Making Changes
 
-If you want to make a contribution, just make a pull request.
+If you want to make a contribution, just make a pull request.
+
+### Code Style
+
+This project uses BiomeJS for linting, and for formatting JS/TS files. Prettier is used for formatting markup files. You can run `npm run lint:fix` to check for linting errors, and `npm run format:fix` to format the files.