Docs overhaul

Docs now include:

- A more thorough introduction
- Core ZeroVM docs, with pretty decent detail (but more work is needed)
- A more thorough ZeroCloud overview
Actually, I do have an idea. The manifest is loaded into memory inside a ZeroVM instance, and as I understand it, a special block of memory with a fixed size is reserved for the manifest. So I guess with the other manifest contents, 10915 channels will eat up all of the available space in the block.