As André mentioned, you don't need to learn a command line tool, or Image Builder, if you'd prefer a GUI interface. Here's a post I just created with step-by-step instructions, since I was taking notes anyway, as I needed to inject 3 VIBs (drivers) into my ISO for my own lab, and it worked out great, took just a few minutes:

Use ESXi-Customer GUI to inject multiple driver VIBs into your ESXi installer ISO

Excerpt:  I’ve often heard that a barrier to giving VMware’s ESXi a try is the burden of figuring out how to inject a driver/VIB file into the installer ISO file. Turns out it isn’t that big a deal, once you locate the GUI utility called ESXi-Customizer. In this video, I add ASMedia SATA, Realtek network, and LSI RAID monitoring support.