Can I giveaway Telltale key?

Steamgifts. Only Steam key or gifts at all times.
So yeah, either setup your own giveaway (using random.org or something) or drop it on the forum.

You can't make a giveaway for a non-Steam game. You can key drop if you want, though I'd suggest not listing it as a pure key due to bots. You can also do a puzzle or perhaps give it with a Steam giveaway.

You can do something like this: http://www.steamgifts.com/discussion/NxZu2/total-war-arena-3-alpha-keys-giveaway
It's still giving away, you simply won't get nice points for it

If you can't read the rules/faq, how will you be able to read responses and advice in this thread?