Add KVM frontend documentation

slapos/recipe/README.kvm_frontend.txt

+kvm_frontend
+===
+
+Introduction
+------------
+
+The ``slapos.recipe.kvm_frontend`` aims to provide proxy server to KVM instances.
+
+It allows HTTPS IPv4/IPv6 proxying (with or without domain name), and supports
+the WebSocket technology needed for VNC-in-webapplication noVNC.
+
+It works following the master/slave instances system. A master instance is
+created, containing all what is needed to run the proxy. Slave instances
+are later created, adding one line in the master instance's proxy configuration
+that specify the IP/port to proxy to the KVM.
+
+The slave instance (kvm) is then accessible from
+http://[masterinstanceIPorhostname]/[randomgeneratednumber]
+
+
+Instance parameters
+------------
+
+Incoming master instance parameters
++++++++
+
+``port``                - self explanatory, mandatory
+``domain``              - domain name to use, optional, default to
+                          "host.vifib.net"
+``redirect_plain_http`` - if value is one of ['y', 'yes', '1', 'true'], instance
+                          will try to create a simple http server on port 80
+                          redirecting to the proxy. Optional.
+
+Incoming slave instance parameters
++++++++
+
+``host``    - KVM instance IP or hostname. Mandatory.
+``port``    - KVM instance port, Mandatory.
+``https``   - if value is one of ['n', 'no', '0', 'false'], will try to connect
+              to target in plain http. Optional.
+
+Connection parameters
+-------------
+
+Outgoing master connection parameters
++++++++
+
+``domain_ipv6_address``  - Proxy IP
+``site_url``             - Proxy URL
+
+Outgoing slave connection parameters are :
++++++++
+
+``site_url``             - URL of instance
+``domain_name``          - Domain name of proxy
+``port``                 - Port of proxy