tsdoc comments and readme for @polywrap/client-js

[krisbitney]

This PR adds comments in the TSDoc format to public methods of the JS PolywrapClient, and adds a readme with full reference documentation based on the comments.

The benefits of this approach:

1. The "Reference" section of the readme is easy to create after copy/pasting the .d.ts file, which contains the comments. Although I did this part manually, it could be automated with a script.
2. We can promote a process wherein developers are expected to update or add tsdoc comments when modifying javascript libraries.

This makes it easy for us to keep reference documentation up to date.

Related:
Documentation Roadmap (hackmd)
Summary of Documentation Roadmap (discord)

Closes polywrap/documentation#206

[dOrgJelli]

This is awesome, I'm all for this approach! Having generated reference documentation to live below the hand-authored example snippets sounds great.

I know that you currently have to copy the generated docs manually now, but this can be its own "snippet" that's embedded using the CLI tool we're going to publish (see here: polywrap/documentation#232).