Document missing package to build for Windows

To build ffmpeg, libz is necessary.

Refs #4955 <https://github.com/Genymobile/scrcpy/issues/4955>

doc/audio.md

@@ -35,7 +35,7 @@ scrcpy --no-video
 # interrupt with Ctrl+C
 ```
 
-Without video, the audio latency is typically not criticial, so it might be
+Without video, the audio latency is typically not critical, so it might be
 interesting to add [buffering](#buffering) to minimize glitches:
 
 ```

doc/build.md

@@ -94,7 +94,7 @@ This is the preferred method (and the way the release is built).
 From _Debian_, install _mingw_:
 
 ```bash
-sudo apt install mingw-w64 mingw-w64-tools
+sudo apt install mingw-w64 mingw-w64-tools libz-mingw-w64-dev
 ```
 
 You also need the JDK to build the server: