Changing the Default Post

I’ve got the multi-site thing working like clockwork and I’m really happy at how easy it was to setup an configure. However, when someone creates a site I’d like for the default post to be something of my own content. Meaning, rather then getting the traditional “Hello World” post I’d like to craft my own welcome message with specific instructions. I’m sure there is a way to do this but can’t seem to find it.

Thanks in advance for any help

Dan