Right prose, wrong place. Notice what else is not here: cppcheck, our static analyzer! Find where the setup for that appears in the docs, and put clang-format there instead.

Just add the package here. It is not preinstalled.

All the instructions in this section should be folded into the Arcanist setup sections for each OS above.

Drop this section, and instead move the commands up into the respective OS-specific Arcanist setup instructions.

Locate how? Remember, the reader won't necessarily know Linux. I know you address this in your comment, but many readers will just stop reading as soon as they don't understand something.

Duplicate these instructions in the Linux, Alternative and macOS sections above.

This won't work as-is for Windows (e.g. locate). You'll need to work out those instructions separately and add them to that section, or else just link to the readme on that morefas-phabricator repository.

I think this would follow a different highlighting. cmd maybe? If in doubt, feel free to use text instead.