Follow-up from "Table of data locations"

Move the section describing the default data directory of various Octez tools (introduced by !106 (merged)) in the main docs section.

This addressed the following discussion from !106 (merged):

• @NicVolanschi started a discussion: (+2 comments)

  Very good initiative to create this clarifying section! So much that it's a pity to have it just available in one of the tutorials (be it a major one). I'd suggest relocating it in the docs part, and linking it here, for two important reasons:

  1. more visibility
  2. we must keep the tutorial short and simple: if you follow just the indicated instructions you don't need to know more details (modulo the warnings that you include here, pointing to the new section)