Changes to slides

thanks a ton, @sarah.diehl

2021/2021-03-18_basicGitTraining/slides/essential_commands.md

@@ -74,7 +74,11 @@ $ git status
 ```bash
 $ git diff
 ```
-exit with `q`
+exit with `q`.
+
+<br>
+
+![bulb](slides/img/bulb.png)  If it is a long diff, you can display additional lines with space.