Uploading a project to Git, readme file?

I read somewhere that whenever someone upload a project to Github, they should always include a readme file, for legal reasons.

What should this readme file say? I dont know much about laws. My project is 100% free and open-source. I use Slick2d(along with LWJGL) and TinySound, the rest have I code myself.

Should I be worried that some douche may sue me?