Reboot before installing ALSA config (google#187)

This allows the correct ALSA state to be configured, and prevents the
volume widget writing an invalid config. Fixes google#183.

HACKING.md

@@ -31,10 +31,21 @@ on Raspbian 2017-07-05 and later. You'll also need to configure ALSA:
 
 ``` shell
 sudo scripts/configure-driver.sh
+sudo reboot
+```
+
+After your Pi has rebooted with the driver enabled, run:
+
+```
+cd ~/voice-recognizer-raspi
 sudo scripts/install-alsa-config.sh
+python3 checkpoints/check_audio.py
 sudo reboot
 ```
 
+Don't skip running `check_audio.py` before rebooting, as it has an important
+effect on the state of ALSA, the sound architecture.
+
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