add BH1750 sensor example

examples/osd/arduino-bh1750/README.md

@@ -0,0 +1,11 @@
+Arduino compatibility example
+=============================
+
+This example shows that it is now possible to re-use arduino sketches in
+Contiki. This example documents the necessary magic. Arduino specifies
+two routines, `setup` and `loop`. Before `setup` is called, the
+framework initializes hardware. In original Arduino, all this is done in
+a `main` function (in C). For contiki we define a process that does the
+same.
+
+See the documentation file in apps/contiki-compat/README.md