samples: net: can: Readme file was missing

The socket CAN application was missing a README.rst file.

Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>

samples/net/sockets/can/README.rst

@@ -0,0 +1,49 @@
+.. _socket-can-sample:
+
+Socket CAN
+##########
+
+Overview
+********
+
+The socket CAN sample is a server/client application that sends and receives
+raw CAN frames using BSD socket API.
+
+The application consists of these functions:
+
+* Setup function which creates a CAN socket, binds it to a CAN network
+  interface, and then installs a CAN filter to the socket so that the
+  application can receive CAN frames.
+* Receive function which starts to listen the CAN socket and prints
+  information about the CAN frames.
+* Send function which starts to send raw CAN frames to the bus.
+
+The source code for this sample application can be found at:
+:zephyr_file:`samples/net/sockets/can`.
+
+Requirements
+************
+
+You need a CANBUS enabled board like :ref:`nucleo_l432kc_board` or
+:ref:`stm32f072b_disco_board`.
+
+Building and Running
+********************
+
+Build the socket CAN sample application like this:
+
+.. zephyr-app-commands::
+   :zephyr-app: samples/net/sockets/can
+   :board: <board to use>
+   :conf: <config file to use>
+   :goals: build
+   :compact:
+
+Example building for the nucleo_l432kc:
+
+.. zephyr-app-commands::
+   :zephyr-app: samples/net/sockets/can
+   :host-os: unix
+   :board: nucleo_l432kc
+   :goals: run
+   :compact: