readme: easy installation instructions

This adds an easy to use one liner for installing the engine into Wineskin.

I decided to use the name `WS9Wine1.7.11NoFlicker` to match how the other engines are named (`WS9Wine1.7.1D3DBoost`, `WS9Wine1.5.25AMDSpeedHack`, `WS9Wine1.5.10NoXInput2`). Figured it was best to go with consistency.

Also, I'm the Linus Unnebäck who uploaded the original patch. Thank you for getting this repository up and running and for taking the time to update and build this!