Update README.md

README.md

@@ -4,12 +4,12 @@ This repository is a modified version of [ORB_SLAM3](https://github.com/UZ-SLAML
 
 --- 
 
-### Modification
+## Modification
 - Succesfully tested in **Ubuntu 20.04** and **ROS2 Foxy**(with OpenCV 4.2.0)
 - Update from C++11 to C++14
 - Fixed unexpected <span style="color:red">error</span> when start **STEREO** mode with **Rectified** camera type  
 
-### How to build
+## How to build
 Clone the repository:
 ```
 git clone https://github.com/zang09/ORB-SLAM3-STEREO-FIXED.git ORB_SLAM3