docs: the bridge, browser, and store that's WIP

[wkillerud]

Depends on changes to the linked PRs and repos.

As part of improving hybrid applications using Podium.

Related repos and branches at time of writing:

• Initial release bridge#7
• feat: listen to and send messages over the Podium JSON RPC bridge if present browser#195
• Publish initial release store#2

As for docs, the most interesting changes are probably the two guides:

• Client-side communication, and how @podium/store lets you do some neat things.
• Hybrid apps, which is still work-in-progress, and what started this whole thing.