Documentation typo in Authorities chapter subheading
Addresses this bugs reported in launchpad:
https://bugs.launchpad.net/evergreen/+bug/1248726

I also browsed through the rest of the docs/admin
directory, and made some (very non-consequential)
changes.

Signed-off-by: Elliot Voris <evoris@slcconline.edu>
Signed-off-by: Robert Soulliere <robert.soulliere@mohawkcollege.ca>