There's no official upstream apt repository/ppa, but there is a package in debian experimental (an unofficial but often outdated ppa for ubuntu exists as well, but there's no v0.5.0 in the stable repository). You can also grab a self-contained binary (an appimage) from https://github.com/neovim/neovim/releases/download/v0.5.0/nv... and then rename it to "neovim", mv it to /usr/local/bin, and chmod +x.