Here's what you should do: download the .txt file, open it, and when you get to the "Edit Signature" page, copy all of the text in the .txt file, and paste it in the signature area. Before doing that, make sure you got rid of the old one. The signature is 450 x 250, so it won't break any rules. And I did the same with mine, just that I have Meganium.
I've decided to make it as a CSS signature instead, since I kinda feel a bit artistic. The signature has a black bg, with purple-dashed border frame. Your username (Gothitelle.) will be in gradient violet-purple text (which is amazing). I'll be using the Gothitelle dreamworld picture.Your user title "Level 100 Fantasy Warrior" (which you're referring to your soon-to-be L100 Gothitelle) will also be used. I think I explained too much to confuse you, did I? lol