Add missing serial comma, per "14.2. Guidelines" of the FDP primer.

[pauamma_gundo.com]

Summary

While there, replace "either" with "one of" which works better for 3 items.

And because I'm feeling generous today, have some insta-filk:

Here's a comma
There's a comma
And another little comma
AP comma
UC comma
Comma comma splice

(TTTO Here's a llama by Weird Al Yankovic)

Test Plan

tested with lynx.

[debdrup]

Comma use looks good to me.