Install packer and dropbox

- [ ] install **[packer][1]** AUR [package manager][2] for ArchLinux
- [ ] via **packer**, install the **[dropbox][3]** package

Resolves: #69 

[1]: https://aur.archlinux.org/packages/packer/
[2]: https://wiki.archlinux.org/index.php/AUR_helpers
[3]: https://aur.archlinux.org/packages/dropbox/