Start docs on compilation process

[gdalle]

@willtebbutt following our discussion on IR, you'll find my notes here. I'm thinking some of them can go into the docs (as a substitute for proper docs of Core.Compiler) and some can go in #337.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

see 37 files with indirect coverage changes

[willtebbutt]

Thanks for these @gdalle -- I'd quite to get them merged into the docs (maybe with some tweaks). It looks like the docs are failing to build at the minute because it thinks that some of your links are invalid.

[gdalle]

Oh right, I think that's because I added these links starting from docs/src but in reality the docs are built from the docs working directory, so there is probably one .. too many. Do you want to remove it and make the necessary rephrasing before merging? My notes are not really mergeable in the current state anyway, so I thought you would want to reformulate and clean them up a bit, possibly correcting inaccuracies.

[willtebbutt]

Sounds good -- are you happy for me to push to this branch directly? (I assume that I can do that...)

[gdalle]

Yeah take it away. But maybe save the remarks about forward mode specifically to the relevant issue before erasing them