Update readme

because:
git clone git@github.com:frdmn/minebackup.sh.git
Cloning into 'minebackup.sh'...
The authenticity of host 'github.com (192.30.252.129)' can't be established.
RSA key fingerprint is 16:27:ac:a5:76:28:2d:36:63:1b:56:4d:eb:df:a6:48.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added 'github.com,192.30.252.129' (RSA) to the list of known hosts.
Permission denied (publickey).
fatal: The remote end hung up unexpectedly