rewrite 'Getting started'
rewrite 'Getting started'

- rename as 'User's Guide'. I intend this page to be the principal reference page for ZettelGeist. In later commits I will absorb what is useful in the tutorials.

- sharpen document structure

- supply synopses of each tool (these may need revision)

- zettel: explain options for saving output to a file

- zettel: explain --load-<FIELD> option

- zettel: explain syntax of --set-cite

- zettel: supply a full list and skeleton description of fields. (This
in part duplicates the page 'Note Format')

- add refs and hyperlinks to Zotero and Better BibTex

- zfind: update options their syntax (use --query-string)

- zfind: output redirection with '>'

ZettelGeist/zettelgeist,ZettelGeist/zettelgeist,ZettelGeist/zettelgeist