README.md: Add example to test

README.md

@@ -3,3 +3,32 @@
 This library provides a "Mouse, Keyboard, and Screen" to Qemu using the
 D-Bus device support in Qemu and GTK 4.
 
+# Testing
+
+By default, Qemu will connect to your user session D-Bus if you do not
+provide an address for `-display dbus`. Therefore, it is pretty easy to
+test things by running Qemu manually and then connecting with the test
+program `./tools/mks`.
+
+```sh
+qemu-img create -f qcow2 fedora.img 30G
+qemu-system-x86_64 \
+    -enable-kvm \
+    -cpu host
+    -device virtio-vga-gl,xres=1920,yres=1080 \
+    -m 8G \
+    -smp 4 \
+    -display dbus,gl=on \
+    -cdrom Fedora-Workstation.iso \
+    -hda fedora.img \
+    -boot d
+```
+
+and then to run the test widget
+
+```sh
+meson setup build
+cd build
+ninja
+./tools/mks
+```