看了OBS官网在MAC上的编译流程
但是卡在下面叙述
NOTE: Qt5 can also be downloaded/installed via the Qt website,
though keep in mind that you will have to set the QTDIR
environment variable to the Qt5 build base directory.
For example: export QTDIR=/usr/local/opt/qt
理解不了这段话的意思
请问这边该怎么做？