add missing info to short-term count docs

[mkewins]

What this pull request accomplishes:

• fills out missing information from category reference table, adds more info
• per request, adds a table that shows the relationship between data loading systems, time availability, and where data lives

Issue(s) this solves:

n/a

What, in particular, needs to reviewed:

• @radumas: added table
• @jwrcoleman: can you give a quick once-over to the category reference table and make sure the info is correct?

What needs to be done by a sysadmin after this PR is merged

n/a