Added a TOC, added a note on VAT (within EU), general edits for legibility.

Clarifying some topics on the accounting page. Mostly just removed superfluous line breaks, corrected typos. Substantive: added a note on VAT for transactions between EU vendors and GitLab BV.

\cc @wilsonlau @pmachle1 @slykahn : I believe these processes are due for reviews and updates especially by Wilson and Sylvia.