Now that you have your picture go to Layers>New Raster Layer and change the blend mode to screen.
Once that's done click the paint brush tool on the left-hand side.
Match your settings to mine, don't worry about the rest:
Choose a color from the colour palette. It's best if you have a bright colour rather than a dull one. Now start to use the brush on the picture.
My result:
It looks kinda cool, doesn't it? :)
I learned a way to make it look even cooler! Go to your background layer and duplicate it. Set that layer on top of Layer 1.
Set your 3rd layer to soft light. And you're done! :D
My result:
