Support installing binaries to the XDG `~/.local/bin`

Currently, atuin requires `~/.atuin/bin` to be added to `PATH`. Would it be possible to install atuin in a way that all binaries go into the XDG standard `~/.local/bin` instead? This would allow skipping the `. "$HOME/.atuin/bin/env"` line altogether on systems that follow the XDG spec and have `~/.local/bin` in `PATH` and avoid adding tool-specific paths. 