update + split README into general and firmware-specific part

firmware/README.txt

@@ -31,3 +31,40 @@ script.  The current runtime environments include
 
 A given software build is made for a specific combination of an APP
 running in a certain ENVIRONMENT on a given BOARD.
+
+A Makefile is provided. It will create output files in the format
+bin/$(BOARD)-$(APP)-$(ENV).{elf,bin}
+
+You can specify the APP and BOARD to build when calling make, like
+e.g.
+* make APP=cardem BOARD=qmod
+* make APP=dfu BOARD=qmod
+
+The level of debug messages can be altered at compile time:
+```
+$ make TRACE_LEVEL=4
+```
+Accepted values: 0 (NO_TRACE) to 5 (DEBUG)
+
+== Flashing
+
+For flashing the firmware, there are at least two options.
+
+=== Using JTAG + OpenOCD to flash the DFU bootloader
+
+The first one is using openocd and a JTAG key.
+For this option, a JTAG connector has to be soldered onto the board, which is not attached per default.
+
+```
+$ openocd -f openocd/openocd.cfg -c "init" -c "halt" -c "flash write_bank 0 ./bin/$(BOARD)-dfu-flash.bin 0" -c "reset" -c "shutdown"
+```
+
+=== Using bossac to flash the DFU bootloader
+
+The second option is using rumba for flashing. No further hardware has to be provided for this option.
+
+FIXME
+
+=== Using DFU to flash application
+
+FIXME