Update import templates & store in more visible location

[pjrobertson]

Right now, import templates can be downloaded from a Helpy Support Page (direct Google Drive link)

However there are 2 issues:

1. This isn't that easy to find. I propose
   1. The docs be stored in this GitHub repo
   2. The help page linked to this GitHub repo
   3. We add an FAQ page to this GitHub repo reiterating how to upload
2. The import templates are incomplete. I note that the 'Docs' and 'Categories' import templates (haven't checked the others) aren't listing all available fields to import.

I've attached two templates here which I've been using to import data into Helpy more conveniently (note: Helpy requires CSV but attached files are XLSX because strangely, Github doesn't support uploading CSV files to issues).
category_import_template.xlsx
docs_import_template.xlsx