Add basic serial console documentation (still needs work).

docs/Serial.md

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+# Using a serial interface with U-boot and libreCMC
+
+A serial interface (console) provides a means of debugging or 
+unlocking features hidden from the user. Most computing devices 
+have a serial interface whether it is broken out by the manufacture or not.
+
+In the case of devices that run libreCMC, a serial console is used
+to configure U-boot and debug libreCMC if the network interface can't
+be brought up. These instructions outline the basics of using
+a serial console with a USB to serial cable.
+
+
+
+## The basics
+
+There are a few different standards for serial interfaces, but here we are
+providing just the basics. There are 3 different connections that we care 
+about : Transmit (TX), Receive (RX) and Ground (GND). Depending on the
+serial cable, the color coding could be different. The common coloration
+is RX is Green, TX is white and GND is black*.
+
+These three wires will be connected to a pin header on the board or might need
+to be soldered to pads. Many device manufactures are kind enough to provide a 
+header and indicate where the serial interface is. Look for silkscreen labeling
+with : GND, TX, RX. Sometimes additional work is needed to break out a stable
+serial interface.
+
+* Many serial cables ship with the color corresponding to the connection on the board, 
+so TX and RX are effectively reversed.
+
+Some routers use the following standard:
+```
+         __________________
+        |            |     |
+        | .   .   .  |  .  |              <- Inside of the router (you may need to do some soldering)
+        |____________|_____|
+                 
+          |   |    \     \
+          *  GND   RX    TX
+```
+
+In this case, transmit is in the marked off box.
+
+```
+         _________________
+        |                 |
+        | .   .   .    .  |             
+      * |_________________|
+
+          |   |    \     \
+        GND   RX    TX   Vcc
+
+```
+
+Some might use a dot to indicate GND, etc...
+
+TPE-R1100 example:
+
+![alt text](images/serial.png "TPE-R1100 Serial")
+
+Warning: NEVER connect the red wire to the device / router! You will most likely fry it because
+many routers use 3.3V for Vcc instead of the 5V provided by USB.
+
+## Getting a console
+
+In order to communicate with the device, we need a terminal application to interact with
+the serial port provided by the USB to serial cable. In this case, we are going to use GNU Screen.
+Make sure that the GNU Screen package is installed and make sure that your user is part of the 
+`dialout` group.
+
+Before we can use the terminal application, we need to know the baud rate at which the serial
+console will be provided at. With most devices running libreCMC and u-boot, this most likely will
+be 115200
+
+## putting it all together
+
+
+1) Plug in / wire up the serial cable to the board.
+
+2) Plug the USB part of the serial cable into an available USB port.
+
+3) run `screen /dev/ttyUSB0 115200` or (if you are NOT part of the `dialup` group) `sudo screen /dev/ttyUSB0 115200`
+
+4) Power on the device you are connecting to.
+
+5) You should see ledgible ASCII text scroll by.
+
+
+# Still needs final review
+