Debian Bullseye needs libx11-dev

Using 2021-10-30-raspios-bullseye-armhf disk image I ended up with an error on `make`

```
/usr/bin/ld: cannot find -lX11
collect2: error: ld returned 1 exit status
make[2]: *** [CMakeFiles/o2m.dir/build.make:258: o2m] Error 1
```

Seems that `libx11-dev` needs to be listed as a dependency.

compile went normally after installing `libx11-dev`