Update README.md

Use the correct domain for the script.
`curl` doesn't follow redirects by default _(at least on my system - Amazon Linux)_, so with the previous instructions the download would silently fail
Fix Debian service restarting

The `service` utility is actually important to use. It does some things like normalize the environment, etc. Directly invoking /etc/init.d/foobar scripts is simply wrong and should not be used.
Adding license file
Merge branch 'patch-1' of https://github.com/strugee/authy-ssh into 538-update-library
Merge branch 'patch-1' of https://github.com/shaneog/authy-ssh into 538-update-library