I couldn't see it mentioned anywhere: https://www.segger.com/downloads/embe…edStudio_Manual
The -I command line option is described on p846 (v4.16), but there is no reference to how it relates to the IDE.
This is probably one of the most frequent beginner questions; eg, just this month in just one forum:
https://devzone.nordicsemi.com/f/nordic-q-a/4…r/190224#190224
https://devzone.nordicsemi.com/f/nordic-q-a/4…e/184681#184681
so it really needs to be clearly described & easy to find.