Allow removing remote old backups with sudo if possible

If allowed by the remote server, try using sudo to remove
old backups (rm needs to be allowed in sudoers to run
without password)

README.md

@@ -68,4 +68,4 @@ sudo --preserve-env=SSH_AUTH_SOCK -s simple_backup [options]
 
 or by editing the sudoers file.
 If SSH key authentication is not available, password authentication will be used instead.
-
+Check the man page for more details.