Polish docs

[Jingru923]

1158 and #1571 are two major doc items we need to address before v1.0. After this I don't think the docs are really v1.0-worthy yet. I cannot now point to concrete chunks, but we probably need some more editing and restructuring.

Tasks:

• [x] #1571
• [x] #590
• [x] #1365
• [x] #1651
• [x] #1463
• [x] #1152
• [ ] Update logos to add D2Hydro and link to NHI (@SnippenE)

[SouthEndMusic]

Automatically detect broken links?

[Jingru923]

All tasks are done so this issue can be closed