Make it clear in this repo’s readme that guide bugs should be submitted to donejs/donejs

When I found bugs in the [quick start guide](https://donejs.com/Guide.html), I searched the [DoneJS org](https://github.com/donejs) for “chat” to see if there was a separate repo for it. Since there was, that’s where I decided to file guide bugs. According to @matthewp, we want guide bugs filed in the [main repo](https://github.com/donejs/donejs), so I think it would be helpful to say that in this repo’s readme.