Better docs on multi-threaded executor

[junderw]

In the same vein as #63 (which was based on v0.1 iirc)

Currently, the docs don't make it clear that "If you have an fn main() {} and you want to start a multithreaded executor and get it running and polling I/O, this is how you do it"

I was trying to find a decisive answer for this person that is upgrading from v0.1 to v2, but I couldn't really find something that makes the same guarantees that smol::run used to (the docs says it used to start a multithreaded and thread local executor.)

https://www.reddit.com/r/learnrust/comments/1eulhti/problem_with_smol_update/

A doc improvement might help in this situation.

If anyone just wants to answer the OP that would help too.

Thanks.

[notgull]

I would accept a PR improving the docs here.

[junderw]

I'm not familiar with smol, but if you can give a 2 sentence blurb of how to do it I can make a PR.

[notgull]

Create an Executor and call run() in block_on() to run the executor, then use spawn() to spawn tasks.

Alternatively, don't worry about it and just use smol-macros to scaffold up to a threadpooled executor immediately.

[junderw]

I'll peek at the expanded output of smol-macros and use it to write some example code for the docs... but I'll be sure to mention the smol-macros crate.