docs: Cleaning up rcx-all.csv table.

Formatted version found in
[SKY130 Stackup Capacitance Data - RCX Model Information](https://docs.google.com/spreadsheets/d/1N9To-xTiA7FLfQ1SNzWKe-wMckFEXVE9WPkPPjYkaxE/edit#gid=1391862914)
sheet.

Signed-off-by: Tim 'mithro' Ansell <me@mith.ro>