Add README.md for Desktop app

[Chhunneng]

The apps/desktop/ folder lacks a README.md. Include:

• Overview of the desktop app
• How to install dependencies (package.json, python-config.json)
• How to run the app (src/main.ts, electron-builder.yml)

[apoorva-as]

i would love to work on this , can u assign me this @vicheanath