Changing repository description in git

You can only change the GitHub repository descriptions of projects which you own. Simple read/write access is not enough to change that. You basically need the same privileges as you need to access the administration section of a project.

The .git\description file is only used in the Git-Web program. Github doesn't even bother about it, and the description that you enter in your local git repo remains local to you and will never be transmitted to the remote repo.

To change project description on Github, look here: How do you change a repository description on GitHub?