chore: Minor updates to BridgeJS documentation

[krodak]

Overview

Some more updates to align existing BridgeJS documentation.

• aligned styling, structure for Exporting to Swift articles, to make it more consistent for the reader. Included some technical explanation in dedicated "How it works" section, so it's a bit more obvious if we copy, use references, etc
• cleaned up a bit technical bridgeJS readme, let me know if that's fine. I remember this being my introduction point for the project, so I thought it could use some attention, might be still useful for potential contributors or folks working on other related projects 🙏🏻

[kateinoigakukun]

Thanks!