install r4 on macOS

Double-click the file you downloaded from Gumroad to unzip it, and open the unzipped folder. Safari may have unzipped it already.
Open a second Finder window, choose Go › Go to Folder, and paste this:
```
~/Library/Audio/Plug-Ins
```
Copy r4.clap into the CLAP folder there, r4.lv2 into LV2, r4.vst3 into VST3, and r4.component into Components, replacing any old copies. Create a folder if it is missing.
When your DAW next scans for plugins, it should find r4.