Add some development guidelines and notes.

HACKING

@@ -10,3 +10,33 @@ http://lxr.linux.no/linux/Documentation/CodingStyle for details.
 
 Please use the same style for any code contributions, thanks!
 
+
+Development guidelines
+----------------------
+
+ - Every new file added must have the usual license header, see the
+   existing files for examples.
+
+ - In general, please try to keep the register and bit naming as close
+   as possible to the official ST datasheets. Among other reasons, this
+   makes it easier for users to find what they're looking for in the
+   datasheets, programming manuals, and application notes.
+
+ - All register definitions should follow the following naming conventions:
+
+   - The #define names should be all-caps, parts are separated by
+     an underscore.
+
+   - The name should be of the form SUBSYSTEM_REGISTER_BIT, e.g.
+     ADC_CR2_DMA, where ADC is the subsystem name, CR2 is the register NAME,
+     and DMA is the name of the bit in the register that is defined.
+ 
+ - All subsystem-specific function names should be prefixed with the
+   subsystem name. For example, gpio_set_mode() or rcc_osc_on().
+
+ - Please consistently use the short form types from <libopenstm32/common.h>,
+   e.g. u8, u16, u32, and so on.
+
+ - 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.
+