docs(master-the-ls): add .sh in the readme

subjects/devops/master-the-ls/README.md

@@ -1,8 +1,8 @@
-## Master the ls
+## master-the-ls
 
 ### Instructions
 
-Create a script `master-the-ls`, that will do the following:
+Create a script `master-the-ls.sh`, that will do the following:
 
 - list the files and directories of the current directory.
 - Ignore the hidden files, the "." and the "..".