update README with development steps

[Harshvardhan Karn]

Add local development section in README with steps:

• to enable Chrome dev tool: console logs, network, source, etc.
• enable hot reloading: to use local ui code without rebuilding

ref: https://www.docker.com/blog/build-your-first-docker-extension/

[ighmaz]

@ibreakthecloud ill do this

[Harshvardhan Karn]

@ibreakthecloud ill do this

sure. Assigned!