update README add costmap image

Author: MaverickPeter

README.md

@@ -12,14 +12,14 @@ Maintainer: Peter XU, [email protected]<br />**
 
 This project was developed at Zhejiang University (Robotics Lab, College of Control Science and Engineering).
 
-<img alt="Elevation Map Example" src="elevation_mapping_demos/doc/cross_road.png" width="700">
+<img alt="Elevation Map Example" src="elevation_mapping/elevation_mapping_demos/doc/cross_road.png" width="700">
 
 ## Loop Performance (Loop version is coming soon)
-<img alt="Elevation Map before loop" src="elevation_mapping_demos/doc/before_loop.png" width="700">
-<img alt="Elevation Map after loop" src="elevation_mapping_demos/doc/after_loop.png" width="700">
+<img alt="Elevation Map before loop" src="elevation_mapping/elevation_mapping_demos/doc/before_loop.png" width="700">
+<img alt="Elevation Map after loop" src="elevation_mapping/elevation_mapping_demos/doc/after_loop.png" width="700">
 
 ## Video
-<a alt="GEM" href="https://youtu.be/MufkLpkNhhY"><img src="elevation_mapping_demos/doc/cross_road.png" width="700" ></a>
+<a alt="GEM" href="https://youtu.be/MufkLpkNhhY"><img src="elevation_mapping/elevation_mapping_demos/doc/cross_road.png" width="700" ></a>
 
 ## Citing
 
@@ -254,6 +254,8 @@ This is the main GEM node. It uses the distance sensor measurements and the pose
 
 **3. Add costmap api for exploration tasks**
 
+<img alt="Elevation Map before loop" src="elevation_mapping/elevation_mapping_demos/doc/costmap.png" width="700">
+