update dev notes

developer-notes.md

@@ -1,18 +1,14 @@
 ## Development building / running
 
-This app is built using Electron. Make sure you have at least node v8 and yarn installed. The app uses ffmpeg from PATH when developing.
+This app is built using Electron. Make sure you have at least node v12 and yarn installed. The app uses ffmpeg from PATH when developing.
 ```
 git clone https://github.com/mifi/lossless-cut.git
 cd lossless-cut
-npm install
+yarn
 ```
 
 ### Running
-In one terminal:
-```
-npm run watch
-```
-In another:
+
 ```
 npm start
 ```