archimedes: Add README

converter/archimedes_usb/README.md

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+Acorn Archimedes Keyboard Converter
+===================================
+This covnerter makes Acorn Archimedes keyboard usable on modern USB computer.
+
+Check these for technical information and resources.
+
+- https://github.com/tmk/tmk_keyboard/wiki/ACORN-ARCHIMEDES-Keyboard
+- https://geekhack.org/index.php?topic=121747.0
+
+
+Preassembled converter is available [here](https://geekhack.org/index.php?topic=72052.0).
+
+
+Pinouts and Wirings
+-------------------
+Mini-DIN-6P female socket from the front:
+
+                    Connector                   AVR pin
+                    ------------------------------------
+      ,--_--.       1: Reset                    PD0
+     / o6 5o \      2: NC
+    | o4   3o |     3: GND                      GND
+     - 2o o1 -      4: 5V                       VCC
+      `-___-'       5: In(from keyboard)        PD1
+                    6: Out(to keyboard)         PD3
+
+Target microcontroller is Atmel ATMega32U2 by default but porting this project to other 8-bit AVR controllers would be easy.
+
+
+Mouse support
+-------------
+Not tested with real mouse but it should work somehow.
+
+I don't have Archimedes mouse to test, try and make a report if you have one.