Fix install extras typo and getting started links

[harveydevereux]

Couple of minor issues one typo in install instructions, but also some dead links to the getting started guide.

Closes #624

[ElliottKasoar]

Can you check the getting started section of the online docs too? I think the extras typo was there too, but I wouldn't be surprised if any links are similarly out of date.

[harveydevereux]

Can you check the getting started section of the online docs too? I think the extras typo was there too, but I wouldn't be surprised if any links are similarly out of date.

Oh yes forgot about that, I did click all the readme links. Could well be some hiding.

[harveydevereux]

Actually @ElliottKasoar does it need to be uv sync --extra all? Not uv sync --extra [extra]?

I guess the last one was you saying the general case: [extra] gets replaced by something. Is it still all that we want there?

[ElliottKasoar]

Actually @ElliottKasoar does it need to be uv sync --extra all? Not uv sync --extra [extra]?

I guess the last one was you saying the general case: [extra] gets replaced by something. Is it still all that we want there?

I think you can argue either way. I'd be inclined to revert back to all since the tests depend on MACE for the most part.

[harveydevereux]

Now uv sync --extra all, and in docs too. I think that is all of them.