Document video chat/streaming/recording options with the Pi 4

I have a couple Logitech C920 webcams, and I wanted to see if I could use them while streaming and/or recording clips at 1080p... the problem is "it's complicated", and unlike macOS where there are literally a dozen or so free options with fancy/simple GUIs for the purpose, on Linux/RPi, it's a lot more complex.

The most _reliable_ way to capture video is with `ffmpeg`, but its usage is inscrutable for beginners. And maybe not impossible for me, but it still requires a lot of futzing around.

After reading [this article about streaming 1080p content to YouTube directly](https://www.arrow.com/en/research-and-events/articles/pi-bandwidth-with-video) (without killing your Pi's poor CPU), it was apparent I was in luck that my Logitech C920 has a built-in H.246 encoder that puts out a pre-compressed stream.

Using this incantation gets the video and dumps it into an mp4 file, with minimal CPU usage:

```
ffmpeg -f v4l2 -codec:v h264 -framerate 30 -video_size 1920x1080 -itsoffset 0.5 -i /dev/video0 -copyinkf -codec:v copy -codec:a aac -ab 128k -g 10 -f mp4 test.mp4
```

Using a simpler/more standard example from ffmpeg's documentation, however, results in the Pi's CPU struggling to maintain 5 fps:

```
ffmpeg -f v4l2 -framerate 30 -video_size 1920x1080 -i /dev/video0 output.mkv
```

You might wonder, 'how do you know the webcam is at `/dev/video0`? Well, find it with:

```
$ v4l2-ctl --list-devices
bcm2835-codec-decode (platform:bcm2835-codec):
/dev/video10
/dev/video11
/dev/video12

bcm2835-isp (platform:bcm2835-isp):
/dev/video13
/dev/video14
/dev/video15
/dev/video16

HD Pro Webcam C920 (usb-0000:01:00.0-1.2.3):
/dev/video0
/dev/video1
```

Now, onto finding a way to get my audio interface into the stream...