Update FS docs

[reynaldichernando]

went through all the APIs, here's some notes:

• space (x) skipped, got 401 when not root
• mkdir (v)
• copy (v) unsure about newMetadata and socket
• move (v) unsure newMetadata, socket, new name don't even work
• rename (v) unsure about socke
• read (v)
• readdir (x) unsure about no thumbs, no assocs, consistency
• stat (v) unsure about consistency
• delete (v)
• upload (v) plenty of stuff left out parsedDataTransferItems, strict, etc, also methods
• write (v) unsure about methods
• sign (x) unsure use case
• symlink (x) unsure use case
• getReadURL (v)