Reduce imgs size

It looks like Photoshop isn't very good with compressing PNGs ;) Solution for https://github.com/netguru/help/issues/65
Before:
![screenshot 2014-05-12 22 06 35](https://cloud.githubusercontent.com/assets/1094422/2949638/f8b82176-da10-11e3-931a-21d6f4f627a1.png)
After:
![screenshot 2014-05-12 22 07 07](https://cloud.githubusercontent.com/assets/1094422/2949645/062d43f4-da11-11e3-8de5-772f1a01c290.png)