Improve package description

Description stolen from the btsync AUR package:
https://aur.archlinux.org/packages/btsync/
Add license files

Installs the following files in /usr/share/licenses/${pkgname}:
 - LICENSE.TXT (from downloaded distribution archive)
 - terms-of-use.html (from link in LICENSE.TXT)
 - privacy-policy.html (from link in LICENSE.TXT)
Move generation of btsync.conf to build()
Use ${pkgname} in reference to bittorrent-sync.install
Add -U and -M options to useradd
Add notice about removing /var/lib/btsync manually

Shamelessly stolen from the btsync package in AUR:
https://aur.archlinux.org/packages/btsync/
Add btsync-makeconfig script

This script generates a default config file for the current user and
prints it to standard out. The script does the following operations:

- Set device name to output of hostname
- Set storage directory to $HOME/.config/btsync
- Set login name to current user's name
Update sha256sum for bittorrent-sync.install
Merge branches 'PKGBUILD' and 'installfile'
Merge branches 'PKGBUILD', 'installfile' and 'services'
Merge branches 'PKGBUILD', 'installfile', 'services' and 'config-script'
fixing file