add example README [skip ci]

examples/README.md

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+### Linux example (Raspberry Pi 3B)
+
+#### Cross compile
+Requirements: 
+```bash
+$ apt-get install -qq gcc-arm-linux-gnueabihf libc6-armhf-cross libc6-dev-armhf-cross
+```
+
+Rustup:
+```bash
+$ rustup target add armv7-unknown-linux-gnueabihf
+```
+To configure the linker use `.cargo/config` file
+
+cross-compile with 
+```bash
+$ cargo build --examples --target=armv7-unknown-linux-gnueabihf
+```
+Copy binary to rpi, once steps below are successfully completed.
+
+#### On RPi (RPi OS lite, 15.02.21)
+
+##### Install i2c dependencies
+```bash
+$ sudo apt-get install i2c-tools libi2c-dev python-smbus -y
+```
+
+##### Enable and load kernel modules at boot
+1. edit `/etc/modules` and add
+    ```
+    i2c-dev
+    i2c-bcm2708
+    ```
+2. edit `/boot/config.txt` and add/uncomment
+    ```
+    dtparam=i2c_arm=on
+    dtparam=i2c1=on
+    ```
+3. reboot
+4. check if working with `sudo i2cdetect -y 1` or `sudo i2cdetect -y 0`. You should bet a signal similar to this
+    ```
+      0 1 2 3 4 5 6 7 8 9 a b c d e f
+    00: -- -- -- -- -- -- -- -- -- -- -- -- --
+    10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
+    20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
+    30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
+    40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
+    50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
+    60: -- -- -- -- -- -- -- -- -- -- -- 68 -- -- -- --
+    70: -- -- -- -- -- -- -- --
+    ```
+5. Wire up 
+
+    | [RPi GPIO](https://www.raspberrypi.org/documentation/usage/gpio/) | MPU6050 |
+    |:---|---:|
+    | 5V Power | VCC |
+    | Ground | GND |
+    | GPIO 2 | SCL |
+    | GPIO 3 | SDA |