Add docs for the Firefox Addons Team

[KarimJedda]

• Add written instructions in the README.md about how to build the extension from a clean VM (dependencies, node version etc)
• Review if there are any minified snippets in the code (double check)

Requirement: "You need to provide the original sources, together with instructions on how to generate the exact same code used in the add-on"

This should get us there I hope ✌️

Related: #1291

[KarimJedda]

More info:

• https://extensionworkshop.com/documentation/publish/add-on-policies/#submission-guidelines
• https://extensionworkshop.com/documentation/publish/source-code-submission/

[polkadot-js-bot]

This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue if you think you have a related problem or query.