This is a full rewrite of the rbt status-update docs, which starts off

by talking about what status updates are and where they're used.
It then provides a full set of descriptions, usage, and options for each

subcommand. These sections provide guidance on the subcommand, showing

how they're used, and demonstrating the standard and JSON output.
The section on setting status updates offers information on what's

needed when creating a status update and what should be provided when

modifying one.
There's also information on upgrading from the old RBTools 1/2 form of

rbt status-update <options> <action> to the new subcommand form.
rbt status-update itself has had two small tweaks made. A help string

has been updated to read better, and deleting a status update now

provides some basic feedback (previously it didn't output anything,

which was confusing).

Built the docs. Read through, checking for bad links, build errors, and

spelling errors.