[Test] remove advertisement

The web doesn't show on Chrome on Android. We test whether it is because of the advertisement.

docs/source/_static/css/custom.css

-
+div.ethical-sidebar {
+    display: none
+}

docs/source/nexuse_repo_instruction.md

@@ -90,6 +90,8 @@ In this section, we assume that you already have Nexus-e codes on Euler, so you
     (1) On Euler, go to the folder where you put the Nexus-e codes. e.g.,  
     ```cd nexus-e```  
     (2) Update all submodules
+      - Delete your local changes  
+      ```git submodule foreach "git reset --hard"```
       - Switch to the master branchs in all submodules  
       ```git submodule foreach "git checkout master"``` 
       - Pull the latest updates in the master branchs