Why not, exactly?
This is a free service, and its features are listed both at the initial page and detailed on the documentation articles. Nowhere was the ability to add such records advertised, so you knew what you were signing up for when you did.
You’re going to have to get specific; we can’t know what’s on your mind.
Regardless, if you have a custom domain (which based on your username, I’m guessing you do), Cloudflare can help you out as Greenreader9 suggested: