I would like to add an additional receptacle(not switched) run from a ceiling light. I just want to make sure I make the right connections in the ceiling light.
Currently in the ceiling light box, there are two 2 wire cables entering the box, 1 from a switch(cable 1) and the other to another rooms light(cable2). The ceiling light is wired as follows:
Cable 1's black wire to the ceiling light black wire, Cable 2's Brown wire(assume it is acting as white) to the lights white wire. Cable 1's White wire connects to Cable 2's Black wire, and the grounds from both cables are connected.

I would like to bring a 3rd 2 wire cable to the ceiling light to connect the new receptacle. How would I wire this to make it hot all the time?

 

That brown wire was probably once white. It has just been discolored. Connect you new cable to cable 2. Match all the colors.
You will have 3 whites together, 2 blacks and a white together. and 3 grounds together.