Link to and improve README for RaspPi

Author: PatrickLang

README.md

@@ -93,6 +93,10 @@ fn HardFault(ef: &ExceptionFrame) -> ! {
 
 ```
 
+### Raspberry Pi
+
+A sample project is available under [examples/raspi](./examples/raspi)
+
 ## License
 
 Licensed under either of

examples/raspi/README.md

@@ -1,8 +1,41 @@
-# raspi demo for oled(ssd1306)
+# SSD1306 demo on Raspberry pi
 
-in rust
+This is a sample that uses the built-in I2C bus available in Linux on the Raspberry Pi B/2/3/4. 
 
-## Quick start
+## Connections
+
+This sample relies on the default [Raspberry Pi pinout](https://www.raspberrypi.org/documentation/usage/gpio/) for i2c:
+
+| Pin |  Description                        |
+|-----|-------------------------------------|
+| 1   | 3.3 v power |
+| 3   | GPIO 2 (SDA) |
+| 5   | GPIO 3 (SCL) |
+| 6   | ground |
+
+
+Some boards such as the [Adafruit OLED bonnet](https://www.adafruit.com/product/3531) use this same pinout if you want something ready to use without extra wiring or soldering.
+
+## OS Configuration
+
+If you're using Raspbian - [raspi-config](https://www.raspberrypi.org/documentation/configuration/raspi-config.md) has an option to enable I2C by default. If you're using another distro - do a quick search and you will probably find a solution to enable it.
+
+Before running this sample, you can check that your OLED display is detected by installing `i2c-tools` from your distro, then running `i2cdetect -y 1`. The first connected SSD1306 will usually be at address `0x3c`. This sample assumes `0x3c`. If your device is at a different address, then you may need to modify the code for it to work.
+
+```
+$ sudo i2cdetect -y 1
+     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
+00:          -- -- -- -- -- -- -- -- -- -- -- -- --
+10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
+20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
+30: -- -- -- -- -- -- -- -- -- -- -- -- 3c -- -- --
+40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
+50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
+60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
+70: -- -- -- -- -- -- -- --
+```
+
+## Building the code
 
 The easiest way to build this sample is with [Cross](https://github.com/rust-embedded/cross). 
 
@@ -24,8 +57,16 @@ Then SSH to your Pi and run it
 sudo ./raspi-oled
 ```
 
-## Example
+## It works!
+
+Once the code is running, it will look like this :)
+
+Commodity SSD1306 boards
+
+![A Raspberry Pi hooked up to a yellow+blue OLED showing the Rust logo](./images/01.jpg)
+
+![A Raspberry Pi hooked up to a yellow+blue OLED showing the IP and some shapes](./images/02.jpg)
 
-![picture](./images/01.jpg)
+Adafruit 128x64 OLED bonnet
 
-![primitive](./images/02.jpg)
+![A Raspberry Pi hooked up to a yellow+blue OLED showing the IP and some shapes](./images/adafruit-oled.jpg)