voice-recognizer.service and HACKING.md are missing in voicekit branch

[t1m0thyj]

In the master branch, the file HACKING.md provides instructions for how to set up a voice recognizer service on the Pi without needing the custom AIY Raspbian image.

Since the master branch is being deprecated and the voicekit branch will soon be the primary one, I switched to using the voicekit branch on my Pi. I noticed that the files for the voice recognizer service are no longer present.

I understand that the new branch is intended to be simpler and easier to build on than the old one, but IMO these files are too useful to be removed. Adding the voice-recognizer.service and HACKING.md files in the new branch would not change the way that this project behaves for anyone who doesn't want to use them, so I don't think it should be a problem to include them.

With these files included, if someone wants to have the voice recognizer service run automatically at boot, all they need to do is run the commands in HACKING.md, copy one of the Python scripts in the src directory and rename it to "main.py", and run "sudo systemctl enable voice-recognizer.service". These are basically the same steps that were needed in the old branch, except the second one is new and now there aren't config files that need to be modified.

I was considering submitting a PR that would add these files back to the new branch and update HACKING.md to mention the new step. But because the voicekit branch is still in development I thought I should create this issue first, to see if an alternative is planned or if such a PR would not be accepted.