Add README.md

README.md

+# BOB3 support library
+
+This library is intended for the [BOB3 educational board](https://www.bob3.org).
+It provides a nice and easy API for all board functions.
+
+
+
+## Getting started
+To write a firmware for BOB3, you need to write a .cpp file containing:
+
+* `#include <BOB3.h>`
+  This allows you to use functions from the library.
+* the function `void setup()`
+  This function is executed during bootup of the chip.
+* the function `void loop()`
+  The function is executed periodically until power is cut.
+
+You may want to start with the example program [example.cpp](example.cpp) and modify it to your liking.
+
+
+
+## Compiling
+To compile the program `example.cpp`:
+
+```sh
+make example.compile
+```
+
+If it works, the output will be a file called `example.hex`.
+
+
+
+## Programming
+To program `example.hex` into the BOB3 MCU:
+
+```sh
+make example.program
+```
+
+This will also automatically (re-)compile `example.hex` if necessary.