ZDoom

I recently decided to create a base for my readme files, I made a .txt file where I can put any informations about the file or application.
But should I really use .txt format? why wouldn't I use rich text format? One reason that comes in my mind is that not every PC supports it but I'm guessing that most shoul do now a days.

Should I delete my txt base file and make one in wordpad or do you recommend something completely different?

If you ever want to upload your work to the /idgames archives, you're going to need to use their readme format - it's not just a formality; the /idgames Database on Doomworld (among other things) actually parses this file, so the format needs to be pretty strict.

That said, including another, fancier instruction manual (if you're interested in writing one) rarely goes amiss.