iOS build instruction.

Update config.h with the correct release version or pick it from a CMake build.

copy the following files at the root dir
cp platforms/ios/config.h .
cp platforms/ios/gcompris.pro .

At root dir create the directory
mkdir rcc
mkdir translations

And fill copy the appropriate files in them.

Create a build directory:
mkdir build-ios
~/Qt/5.5/ios/bin/qmake ../gcompris.pro
open gcompris.xcodeproj

Fix the Launch reference to point the Launch item in the xcassets