Add entry for Cirrus runners (https://tart.run)

[neysofu]

See https://tart.run/integrations/github-actions/.

[fkorotkov]

Hi @neysofu, one of engineers working on Cirrus Runners here. I'd be happy to add an entry for Cirrus Runners. Is there any particular rules for ordering and adding ⭐️ emoji?

[neysofu]

Hi @fkorotkov, I'd be very happy to review your PR! I'm using the stars as a way to highlight what I personally believe are the best and most mature products in the space. This is, of course, subjective, but I strive to be as impartial as possible and fair to all entries. I'm thinking we can add Cirrus Runners between Blacksmith and Ubicloud, and then I'll make sure I go through your docs, reviews, case studies as well as play around with it to determine if want to place it higher up in the list, or even to give it a star. How does that sound?