Add Red Crackle to Planet Drupal

The feed passes validation.

I thought I had remembered seeing them show up in the Planet Drupal feed before, and it looks like they were added in 2015 (see #2423333: Add Red Crackle to Planet Drupal) but later in that issue (comment 6 in 2017, #2423333-6: Add Red Crackle to Planet Drupal), it says "Feed removed for lack of cooperation." (although there isn't much detail about what went into that decision).

@mparker17 Thank you for pointing that out!

Fo what I can read from #2548575: Posts from Red Crackle on Planet are showing in the future, at 7:20 AM (GMT), a post from that feed was reported as posted at 9:25 PM.
I am not sure that would be a reason to remove the feed from Planet Drupal. I would be more worried about a lack of replies when the feed content were inappropriate for Planet Drupal because, for example, offensive phrases.

The article summary should be between 600 and 1000 characters. There aren't posts published in the past 3 months and three weeks, which means none of them would appear on Planet Drupal.

I added the feed to Planet Drupal (https://www.drupal.org/aggregator/sources/1993).