Will Libreddit support signing into a Reddit account?
It may eventually but this feature is not planned.
How can I show my support?
I'm glad you like Libreddit! :) You can contribute by submitting bugs, contributing code, or donating to the Bitcoin and Monero addresses listed in the README. ♥
Libreddit doesn't have an API or any RSS feeds because most of Libreddit's benefits come from the web interface (faster speeds, no ads, less resources loaded, etc.) so there really wouldn't be any advantage to using a Libreddit API/RSS feed over a proxied Reddit API/RSS feed. If you do need a something of that nature, I'd recommend taking a look at Teddit's API.