Merge pull request #200 from mirguest/master

update the docs.

docs/quickstart.md

 # Quick start
 
-## Start development environment in a Singularity Container
+## Start development environment in lxslc7 (CentOS 7)
 
-Start the container in lxslc7 (OS: CentOS7):
 ```
-$ /cvmfs/container.ihep.ac.cn/bin/hep_container shell SL6
+$ ssh -Y USERNAME@lxslc7.ihep.ac.cn
 ```
 
 ## Manage code using git

docs/tutorial.md

 # Tutorial
 
-* [New CEPCSW Tutorial and detector study, IHEP, 17-18 Sept 2020](https://indico.ihep.ac.cn/event/12341/)
-  * [Tutorial on CEPCSW simulation](https://cepc.github.io/CEPCSW/simulation-tutorial/index.html#/)
+* [CEPCSW Tutorial and detector study, IHEP, 17-18 Sept 2020](https://indico.ihep.ac.cn/event/12341/)