Unable to build driverbeat following the parser_setup.md

[zisenXu]

There is one mistake in parser_setup.md. The variable LIB_INSTALL_PATH=$PWD is ShadeWatcher/lib. While building the gcc-8.4.0, the param --prefix is set to $LIB_INSTALL_PATH/lib. Therefore, the target directory of building the gcc is ShadeWatcher/lib/lib and the executable will be generated in ShadeWatcher/lib/lib/bin.
So, the system path should be set as echo export PATH=$LIB_INSTALL_PATH/lib/bin:$PATH >> ~/.bashrc, instead of echo export PATH=$LIB_INSTALL_PATH/bin:$PATH >> ~/.bashrc. In this way, the building process could find the correct complier.