Add existing project steps

Author: jccit

README.md

@@ -8,11 +8,26 @@ This project adds a JS build step similar to what you would find in a modern web
 
 ## How to use
 
+### New project
+
 1. Copy this project
 2. Change the name, author and uuid in package.json
 3. Install dependencies `npm install`
 4. Build the app like normal, `pebble build` will compile your TypeScript and your Pebble app
 
+### Existing project (advanced)
+
+You can convert an existing PKJS to PKTS by copying a few files and making some config changes.
+
+If you run into any issues I'd recommended following the "New Project" instructions and copying your existing C code into the new project.
+
+1. Copy `babel.config.json`, `rollup.config.mjs`, `tsconfig.json`, `wscript` into your app, overwrite any existing files
+2. Copy the `scripts`, `dependencies` and `devDependencies` from `package.json` into your project's `package.json`
+3. Copy the `src/ts` folder to your project
+4. Update `src/ts/index.ts` with your app's code. This is just the entrypoint so feel free to split your code using modules
+5. Install dependencies `npm install`
+6. Build the app like normal, `pebble build` will compile your TypeScript and your Pebble app
+
 ## Available types
 
 - `ready` and `appmessage` events