The note can be found in Beckley, on a rooftop table with a parasol.
If you're reading this get out while you still can. The miners have started destroying the robots and it's only a matter of time before Hornwright steps in to protect his assets.
Mitchell heard that the military is on their way so a few of us are heading to the Mount Blair train station. We heard that there are trains taking people out of the city. I suggest you head there too.