If you have to ask for a guide, you probably shouldn't be doing it.
Script is here:
https://github.com/ajd4096/inject_gba
Of 2810 roms, 2810 can be injected.
On an N54L, that took about 2.5 hours and used about 118G
(find|xargs is your friend)
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To install (needs python3)
python setup.py...