Updated Code of conduct (markdown)

Code-of-conduct.md

@@ -2,3 +2,14 @@
 
 
 
+### 1. The file shebang must be `sh` not `bash`
+
+    acme.sh is a `unix shell` script,  not just a `bash` script.
+
+    If you want to contribute your script, the shebang must be: 
+    ```sh
+    #!/usr/bin/env sh
+    ```
+    After the installation, acme.sh could change the shebang to bash to get better performance if you have bash on your machine.
+
+    Of course, if you just use it on your own, it can be any valid shebang on your machine. It could be `sh` or `bash`, it's up to you.