wscript: set rpath to current folder, LD_LIBRARY_PATH is unneeded anymore

Fix README and AppImage launch script accordingly

game_launch/wscript

@@ -37,6 +37,7 @@ def build(bld):
 		features = 'c cxx cxxprogram',
 		includes = includes,
 		use      = libs,
+		rpath    = '.',
 		install_path = bld.env.BINDIR,
 		subsystem = bld.env.MSVC_SUBSYSTEM
 	)