Since Manjaro is Arch based, the same path can be used.
Tested in Manjaro 18.1.5 by manually installing the listed archlinux packages.
$ stegoveritas file.png
ERROR:StegoVeritas:Missing the following required packages: exiftool, foremost
ERROR:StegoVeritas:Either install them manually or run 'stegoveritas_install_deps'.
$ stegoveritas_install_deps
ERROR:stegoveritas.install_deps:Unhandled distribution to install deps: manjaro linux
ERROR:stegoveritas.install_deps:Please poke me or submit a PR.
Since Manjaro is Arch based, the same path can be used. Tested in Manjaro 18.1.5 by manually installing the listed archlinux packages.