Add tutorial on how to use Workers KV directly from Rust

[fkettelhoit]

During a call with @Albertozhao today he mentioned that a code sample showing how to use Workers KV directly from a Rust worker could be a suitable addition to the existing docs. This PR is a tutorial that shows how to wrap a subset of the Workers KV API in rust and use it to create a worker that exposes simple get and put operations, with the following end result:

$ curl 'localhost:8787/foo'
""
$ curl -X PUT 'localhost:8787/foo?value=bar'
$ curl 'localhost:8787/foo'
"bar"

[kristianfreeman]

this is awesome!! do you mind doing a soft wrap instead of hard wrap throughout this file? will make it easier to review. we'll rope in some members of the team to check this out once i can take an initial look

[fkettelhoit]

@signalnerve sure, done!

[fkettelhoit]

By the way, the following PR might also be relevant in the context of Rust workers: cloudflare/wrangler-action#61

(I'm mentioning it here since I wasn't sure how actively the wrangler-action repo is being maintained.)

[deadlypants1973]

Adding in my notes for style guide revision.

[kristianfreeman]

Is there an example repo that can be linked down here in a conclusion paragraph?

[fkettelhoit]

I have now pushed the full example to https://github.com/fkettelhoit/workers-kv-from-rust and added a short note in the last paragraph. Feel free to move the code over to some Cloudflare repository, if you would prefer not to link to external repositories.

[deadlypants1973]

final review comments

[deadlypants1973]

Approved from style guide review but need @signalnerve to give final okay.