docs: add more documentation to each of the modules in vlib (#13043)

vlib/sokol/README.md

@@ -4,3 +4,54 @@
 which in turn is a library of "Simple STB-style cross-platform libraries
 for C and C++, written in C.", that provide access to graphics/audio/input
 processing.
+
+Each `.h` file in the sokol source code is well-documented as can be seen here:
+
+[sokol_audio.h](https://github.com/floooh/sokol/blob/master/sokol_audio.h)
+
+## Example from `@VROOTDIR/examples/sokol/sounds/simple_sin_tones.v`:
+
+```v
+import time
+import math
+import sokol.audio
+
+const (
+	sw          = time.new_stopwatch()
+	sw_start_ms = sw.elapsed().milliseconds()
+)
+
+[inline]
+fn sintone(periods int, frame int, num_frames int) f32 {
+	return math.sinf(f32(periods) * (2 * math.pi) * f32(frame) / f32(num_frames))
+}
+
+fn my_audio_stream_callback(buffer &f32, num_frames int, num_channels int) {
+	ms := sw.elapsed().milliseconds() - sw_start_ms
+	unsafe {
+		mut soundbuffer := buffer
+		for frame := 0; frame < num_frames; frame++ {
+			for ch := 0; ch < num_channels; ch++ {
+				idx := frame * num_channels + ch
+				if ms < 250 {
+					soundbuffer[idx] = 0.5 * sintone(20, frame, num_frames)
+				} else if ms < 300 {
+					soundbuffer[idx] = 0.5 * sintone(25, frame, num_frames)
+				} else if ms < 1500 {
+					soundbuffer[idx] *= sintone(22, frame, num_frames)
+				} else {
+					soundbuffer[idx] = 0.5 * sintone(25, frame, num_frames)
+				}
+			}
+		}
+	}
+}
+
+fn main() {
+	audio.setup(
+		stream_cb: my_audio_stream_callback
+	)
+	time.sleep(2000 * time.millisecond)
+	audio.shutdown()
+}
+```