Change project description to make it clear external session stores can be used
We were using a different session module. I never looked at `koa-session` because the description sounds like it only supports cookies (we use Redis). Turns out, it’s easy to plug Redis into `koa-session`.

It would be helpful to edit the project description on Github and `package.json` so dummies like me will give this a try. This is the most-downloaded Koa session middleware and should be the go-to module for all session needs.