docs(networking): expose machine basic description

docs/docs/expose_machine.rst

+Exposing a Virtual Machine
+==========================
+
+By default the virtual machines are created inside a private internal
+network. This allows the user to reach internet but no connections
+from outside are allowed.
+
+Some times we may want to install a server in the Virtual Machine and
+grant access to it. There are many ways to expose a Virtual Machine and
+allow access to it from outside. Here we describe a few: set a public IP
+address, redirect with IPTables and HTTP forwarding.
+
+Setting a public IP
+-------------------
+
+One way to expose the virtual machine is use a public IP instead the
+private used by default. To do so you have to manually edit the machine
+definition before creating the base. Change the network settings to
+`bridge <https://www.linux-kvm.org/page/Networking>`_.
+
+This setting gives the more exposure to the virtual machine, so firewalls
+and other security measures must be configured.
+
+IPTables redirection
+--------------------
+
+You can redirect a port from the host or a virtual machine acting as
+gateway to the internal address of the machine you want to expose.
+
+This technique restricts which ports from the internal machine are
+exposed from outside.
+
+
+HTTP Forwarding
+---------------
+
+HTTP forwarding can be configured in a web server in the host to access internal web
+services from outside.