HACKING: Document the examples/ directory layout.

HACKING

@@ -40,3 +40,14 @@ Development guidelines
  - Variables that are used to store register values read from registers or
    to be stored in a register should be named reg8, reg16, reg32 etc.
 
+ - In the examples directory, the following structure should be used:
+
+    - One (or more) subdirectories for the type of microcontroller, e.g.
+      lm3s, lpc13xx, stm32/f1, stm32/f2, stm32/f4.
+
+    - One subdirectory in there for each eval board or piece of hardware, e.g.
+      stm32-h103, lisa-m, stm32vl-discovery, stm32f4-discovery, etc.
+
+    - One subdirectory in there for each example, e.g.
+      miniblink, button, usart, usb_dfu, etc.
+