Added HW documentation in README

README.md

@@ -1,8 +1,9 @@
 # Motenpoche
 
-Motenpoche ([mot-ɑ̃-pɔʃ] - French for "word in your pocket") is a physical password
-vault to carry around your secrets securely. It can be unlocked with a main
-passphrase and it will automatically paste passwords selected from your collection.
+Motenpoche ([mot-ɑ̃-pɔʃ] - like in *"Mot en poche"*, French for "word in [your] pocket")
+is a physical password vault to carry around your secrets securely. Once connected
+to a PC and unlocked with a main passphrase and it will automatically paste
+passwords selected from your collection.
 
 Passwords can be provisioned with the help of a host-side command line tool that
 can be run on a GNU/Linux PC.
@@ -33,6 +34,34 @@ around (and lost, or forgotten on a public transportation...) with reduced risk.
 
 ## Hardware design
 
+The design is based on the rp2040 "Raspberry Pi Pico" board, with a few components
+and peripherals connected as shown here:
+
+![motenpoche schematic](doc/png/motenpoche_sch.jpg)
+
+
+### Pinout
+
+Here is a recap of the pins used on the Raspberry PI, as configured by the
+software in this repository:
+
+| Pin | Function | Connects to | Pullup/pulldown |
+| --- | -------- | ----------- | --------------- |
+| GPIO2 | FUNC\_SPI    | SPI Flash SCLK   | none |
+| GPIO3 | FUNC\_SPI    | SPI Flash MOSI  | none |
+| GPIO4 | FUNC\_SPI    | SPI Flash MISO   | none |
+| GPIO5 | OUT    | SPI Flash CS  | none |
+| GPIO16 | OUT | Green LED cathode  | none |
+| GPIO17 | OUT | Red LED cathode  | none |
+| GPIO18 | IN  | Rotary Keypress  | pull-up |
+| GPIO19 | IN  | Rotary S1  | pull-down |
+| GPIO20 | IN  | Rotary S2  | pull-down |
+| GPIO21 | IN  | Pushbutton "Back"  | pull-down |
+| GPIO22 | IN  | Pushbutton "Confirm"  | pull-down |
+| GPIO26 | FUNC\_I2C   | I2C Display SDA | none (automatic pull-up) |
+| GPIO27 | FUNC\_I2C   | I2C Display SCL | none (automatic pull-up) |
+
+
 ## How it works
 
 The siple idea behind it is that the device does not carry any secret in plain