migrate: Support doas, support port, use user@host:port syntax

docs/chapters/migration.rst

@@ -19,6 +19,9 @@ must be able to log in via SSH using either key-based authentication, or passwor
 The user also needs ``sudo`` permissions on the remote system. This user should then be given as the
 ``USER`` arg in the ``migrate`` command.
 
+If you don't want to use ``sudo``, we support using ``doas`` as the super-user command. Simply set ``--doas`` as
+one of the options when running the ``migrate`` command.
+
 If you are using key-based auth, the keys should be stored in the default location at ``$HOME/.ssh/id_rsa``,
 where ``$HOME`` is the users home directory. This is the default location for ssh keys, and where Bastille
 will try to load them from.

docs/chapters/subcommands/migrate.rst

@@ -6,14 +6,23 @@ another remote system. See the chapter on Migration.
 
 This sub-command supports multiple targets.
 
+Syntax for the remote system is ``user@host``. You can also specify a non-default
+port by supplying it as in ``user@host:port``.
+
 .. code-block:: shell
 
   ishmael ~ # bastille migrate help
-  Usage: bastille migrate [option(s)] TARGET USER HOST
+  Usage: bastille migrate [option(s)] TARGET USER@HOST[:PORT]
+  
+    Examples:
+
+    bastille migrate attica migrate@192.168.10.100
+    bastille migrate attica migrate@192.168.1.10:20022
 
     Options:
 
     -a | --auto              Auto mode. Start/stop jail(s) if required.
     -d | --destroy           Destroy local jail after migration.
+       | --doas              Use 'doas' instead of 'sudo'.
     -p | --password          Use password based authentication.
     -x | --debug             Enable debug mode.