Add interrupt section to docs

[earlephilhower]

Adds a section on interrupts to the docs and lists the restrictions
and warnings about running long tasks.

Fixes #6428

[devyte]

I believe there were some comments about slme of this already in section "why does my esp crash". It might be a good idea to cross check against that.

[earlephilhower]

Updated w/your proofreading and requests.

I believe there were some comments about slme of this already in section "why does my esp crash". It might be a good idea to cross check against that.

The FAQ does have a section on Interrupts, too, but I though it would be better to make the IRQ restrictions front-and-center before things crash, too. The contents are pretty close and don't contradict each other.

If you're really against it, I can drop the section in the reference.rst and just add a the bit about memory allocation in the FAQ bit.

[devyte]

Oh, I'm completely in favor of this. Users have missed the current section enough times that I think an additional specific section would be beneficial, even if the info is duplicated.
What I meant was to check for contradictions, which you already did, and missed info in the other section that could be added here, e. g. timing constraints.

[devyte]

I'm ok with this.