[add] example shell for turtlebot4 with gz-ros and nav2

examples/ros2-turtlebot4-gz.nix

@@ -0,0 +1,26 @@
+# Environment containing basic ROS2 tools
+
+{ pkgs ? import ../. {} }:
+with pkgs;
+with rosPackages.jazzy;
+
+mkShell {
+  nativeBuildInputs = [
+    (buildEnv {
+      paths = [
+        ros-core
+        colcon
+        geometry-msgs
+        turtlebot4-desktop
+        turtlebot4-simulator
+        slam-toolbox
+        nav2-minimal-tb4-sim
+        nav2-minimal-tb3-sim
+        # rqt metapackages
+        rqt-common-plugins
+        rqt-tf-tree
+        tf2-tools
+      ];
+    })
+  ];
+}