Having trouble installing and writing rules on Snort w/ Mac

Question

I installed Snort on my Mac Mojave v. 10.14.5, but am having difficulty installing the rules. First, I installed Snort on my terminal with the command "brew install snort." Then I ran into a set of directions online saying that in order to get the rules file, I needed to download snortrules-snapshot-2970.tar.gz. I did that, but the problem comes when the package needs to be copied into the /usr/src directory. I have a usr folder, but there is no src inside of it. So I tried creating an src folder, but the computer won't let me drag it into usr. I can't create the folder directly in usr either.

What am I supposed to do? Is there another way to get the rules file or manually write rules? I've also looked around on the internet and am extremely confused as to where you're supposed to manually write the rules. Nothing I've found so far says where you're supposed to do it. I tried doing so on snort itself in the terminal, but it doesn't work. If I stop the program with Control-C, it exits completely, so there's no way to enter the rules there. I assume the rules need to be entered with different code on the terminal? Any help would be most appreciated.