demo: renamed demo folder to sample, updated readme

sample/ranger_demo/CMakeLists.txt

@@ -0,0 +1,2 @@
+add_executable(demo_ranger_robot ranger_robot_demo.cpp)
+target_link_libraries(demo_ranger_robot ugv_sdk)

sample/ranger_demo/ranger_robot_demo.cpp

@@ -0,0 +1,57 @@
+/**
+ * @Kit       : Qt-Creator: Desktop
+ * @Author    : Wang Zhe
+ * @Date      : 2021-04-19  19:41:52
+ * @FileName  : ranger_demo.cpp
+ * @Mail      : wangzheqie@qq.com
+ * Copyright  : AgileX Robotics
+ **/
+
+#include "ugv_sdk/mobile_robot/ranger_robot.hpp"
+
+using namespace westonrobot;
+
+int main(int argc, char *argv[]) {
+  std::string device_name;
+
+  if (argc == 2) {
+    device_name = {argv[1]};
+    std::cout << "Specified CAN: " << device_name << std::endl;
+  } else {
+    std::cout << "Usage: app_ranger_demo <interface>" << std::endl
+              << "Example 1: ./app_ranger_demo can0" << std::endl;
+    return -1;
+  }
+
+  RangerRobot ranger;
+  ranger.Connect(device_name);
+
+  ranger.EnableCommandedMode();
+
+  int count = 0;
+  while (true) {
+    if (count < 100) {
+      std::cout << "Motor: 0.2, 0" << std::endl;
+      ranger.SetMotionCommand(0.2, 0.0);
+    }
+
+    auto state = ranger.GetRobotState();
+    std::cout << "-------------------------------" << std::endl;
+    std::cout << "count: " << count << std::endl;
+    std::cout << "control mode: "
+              << static_cast<int>(state.system_state.control_mode)
+              << " , vehicle state: "
+              << static_cast<int>(state.system_state.vehicle_state)
+              << std::endl;
+    std::cout << "battery voltage: " << state.system_state.battery_voltage
+              << std::endl;
+    std::cout << "velocity (linear, angular): "
+              << state.motion_state.linear_velocity << ", "
+              << state.motion_state.angular_velocity << std::endl;
+    std::cout << "-------------------------------" << std::endl;
+
+    usleep(20000);
+    ++count;
+  }
+  return 0;
+}