[docs] Fleshed out Move docs using sui-move CLI a bit more

[awelc]

Rewritten the Move-related docs describing how to write/test Move code with sui-move CLI to better match the overall structure of the docs.

I also fleshed out the doc a bit more, adding description of structs and documentation on how to write and build a simple module.

[sblackshear]

So helpful, thank you!!

[sblackshear]

Coin is somewhat of an unfortunate starting point because we have to explain both generics and phantom off-the bat... No concrete suggestions for alternatives + totally ok going forward with this, just registering the thought.

[awelc]

I was thinking of what the starting point could be that would still work with the wallet part that I already wrote, and also involved just looking at our framework code rather than starting with code writing. I agree that this is a little dense, but I could not come with something obviously better and at least Coin is a familiar concept.

[sblackshear]

Suggested change

	also have the `key` ability used to enforce existence of the `id`
	also have the `key` ability (which allows the object to be persisted in Sui's global storage)

[awelc]

What is store ability for then?

[awelc]

I have rewritten it according to the suggestion, and left out description of the store ability, but I am still confused why we need store then if we already have key. I makes some sense to me in Diem Move and its docs, but if I remember correctly, we re-purpose the key ability in Sui a bit - is it still about only being able to use store operations (e.g., transferring ownership from one address to another) if a struct has the key ability but not if it only has store ability?

[sblackshear]

CC @lxfind who has ideas about relaxing these rules (and we could perhaps avoid explaining them if that change will go in soon, or remember to update this doc later if not)

[awelc]

I know we have been musing about it, but I figure I should record the current state of the world for now - I am pretty sure this is not going to be the only change to the docs we will have to make in the future.

[Clay-Mysten]

You can make this link relative and avoid the named anchor, like so:
(objects.md)

[awelc]

Sure thing! I think I just pasted int the URL without thinking here...

[Clay-Mysten]

It would be good to highlight what aspects of the central Move docs are inapplicable here if we don't describe in detail below.

[awelc]

I think it's a little tough to specify, and certainly creating an exhaustive list here would be difficult. The point of this statement is that it is best to simply follow this tutorial and relevant Move documentation links provided in the tutorial rather than diving into "general" Move docs. I added a sentence to this effect, but also an example of a difference between Sui Move and "standard" Move.

[Clay-Mysten]

arguments pass

[awelc]

It was meant to be "passed"

[Clay-Mysten]

that cannot

[awelc]

See above comment. The whole sentence now reads (with another small typo fix - "instance" instead of "instances"):

"Move's type system enforces an invariant that struct instance arguments passed by read-only references (as opposed to mutable references) cannot be modified in the body of a function (you can read more about Move references here)"

[Clay-Mysten]

Fantastic work, Adam! I pointed out a few issues and will do a more thorough edit myself once you have finished your set of changes. Thanks!