docs: Improve dev guide's installation and firmware flash instructions.

docs/devguide/flashfirmware.rst

@@ -36,15 +36,22 @@ targets.
 Preparing firmware and a Python program
 ---------------------------------------
 
-tools/makecombined
-
-hexlify
+A script in the following location, called using the following syntax, should
+help::
 
+  tools/makecombinedhex.py <firmware.hex> <script.py> [-o <combined.hex>]
 
+The script will output to ``stdout`` if no output option (``-o``) is provided.
 
 Flashing to the micro:bit
 -------------------------
 
+The Microbit mounts itself as a mass storage device over USB.  When it detects
+that a .hex file has been uploaded to the internal mass storage device, it will
+flash itself with the bytecode representation, and start running the program.
+
+This means that uploading a .hex file should result in the Microbit running your
+code.
 
 
 

docs/devguide/installation.rst

@@ -75,14 +75,22 @@ Debian/Ubuntu, and Red Hat Fedora/Centos.
 Debian and Ubuntu
 ^^^^^^^^^^^^^^^^^
 
-::
+The following commands should install the toolchain on a modern Debian/Ubuntu
+variant::
 
   sudo add-apt-repository -y ppa:team-gcc-arm-embedded
   sudo add-apt-repository -y ppa:pmiller-opensource/ppa
   sudo apt-get update
   sudo apt-get install cmake ninja-build gcc-arm-none-eabi srecord libssl-dev
   pip3 install yotta
 
+In order to make development life a bit easier, you can (on Ubuntu) add yourself
+to the ``dialout`` group, which grants write access to the serial device
+``/dev/ttyACM0``::
+
+  sudo usermod -a -G dialout ${USER}
+
+You may need to relogin in order for the changes to groups to take effect.
 
 .. _microbit-redhat: