docs: Update README.md on install gcc10

Author: Kin-Zhang

README.md

@@ -15,16 +15,15 @@ Quick Demo: Run with the **same parameter setting** without tuning for different
 ## 0. Setup
 
 ```bash
-sudo add-apt-repository ppa:ubuntu-toolchain-r/test
-sudo apt update && apt install gcc-10 g++-10
+sudo apt update && sudo apt install gcc-10 g++-10
 sudo apt install libtbb-dev liblz4-dev
 ```
 
 Dockerfile will be soon available.
 
-Clone and init submodules:
+Clone quickly and init submodules:
 ```bash
-git submodule update --init --recursive
+git clone --recursive -b main --single-branch https://github.com/KTH-RPL/dufomap.git
 ```
 
 ## 1. Build & Run