Rework README and documentation

The README.md page is HUGE. Split it up.

Also document audio forwarding and improve installation instructions for
each platform and user documentation.

PR #3774 <https://github.com/Genymobile/scrcpy/pull/3774>

doc/recording.md

@@ -0,0 +1,44 @@
+# Recording
+
+To record video and audio streams while mirroring:
+
+```bash
+scrcpy --record=file.mp4
+scrcpy -r file.mkv
+```
+
+To record only the video:
+
+```bash
+scrcpy --no-audio --record=file.mp4
+```
+
+_It is currently not possible to record only the audio._
+
+To disable mirroring while recording:
+
+```bash
+scrcpy --no-display --record=file.mp4
+scrcpy -Nr file.mkv
+# interrupt recording with Ctrl+C
+```
+
+Timestamps are captured on the device, so [packet delay variation] does not
+impact the recorded file, which is always clean (only if you use `--record` of
+course, not if you capture your scrcpy window and audio output on the computer).
+
+[packet delay variation]: https://en.wikipedia.org/wiki/Packet_delay_variation
+
+The video and audio streams are encoded on the device, but are muxed on the
+client side. Two formats (containers) are supported:
+ - Matroska (`.mkv`)
+ - MP4 (`.mp4`)
+
+The container is automatically selected based on the filename.
+
+It is also possible to explicitly select a container (in that case the filename
+needs not end with `.mkv` or `.mp4`):
+
+```
+scrcpy --record=file --record-format=mkv
+```