Add Rust on Espressif discovery journey

[SergioGasquez]

Hi! Since we at Espressif have something similar to the discovery books, but in a different format, I thought that it might be worth mentioning the resources in the discovery book.

If you want to keep this for the current content only, feel free to close the PR. Also, not sure if the format in which I added it, is the best, so also open to any suggestions!

[hdoordt]

This feels a bit out of place to me. I think a reference like this is more fit for an entry in Awesome Embedded Rust. Which, as it turns out, it already is

[sirhcel]

Wow, this got closed pretty fast. I would still advocate for including a reference in the Discovery Book for the following reasons:

• At RustNL we discussed to cover sync and asnyc embedded Rust in the discovery book, so at least referring to the "second dimension" of of embedded Rust - no_std and std - feels natural to me
• Especially the RISC-V devices offer a comfortable way of getting into embedded Rust and they are well supported and easily accessible targets
• Awesome Embedded Rust is really broad and overwhelming for "young players" and I from my perspective these two points (std + sync, std + async) in the design space could and should be mentioned in the Discovery Book as well
• Training resources are already available

Documentation and the Discovery Book is currently under discussion. What about discussing the if, how and where there as well?

[SergioGasquez]

I guess Ill reopen it for others to jump in an give an opinion

[eldruin]

I get this is slightly out of place because the relationship is not clear. We also do not link to the rust embedded book here (but maybe we should!). Otherwise this seems fine to me.
I think adding an "Alternatively" or similar word might be an improvement.