docs(master-the-ls): moving the subject to the folder devops and fix readme

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

@@ -10,14 +10,23 @@ Put in a file `master-the-ls`, the command line that will:
 - Order them by ascending order of access time (the newest first).
 - Have the directories ends with a `/`.
 
-### Hint
+### Hints
 
 Here are some Commands that can help you:
 
-- `tr`. Translate characters: run replacements based on single characters and character sets.For more information: https://www.gnu.org/software/coreutils/tr.
+- `tr`. Translate characters: run replacements based on single characters and character sets.
 
   - Replace all occurrences of a character in a file, and print the result:
     `tr {{find_character}} {{replace_character}} < {{filename}}`
 
-- `ls`. List directory contents. For more information: https://www.gnu.org/software/coreutils/ls.
-- `sed`. Edit text in a scriptable manner. You can see also: awk. For more information: https://www.gnu.org/software/sed/manual/sed.html.
+- `ls`. List directory contents.
+- `sed`. Edit text in a scriptable manner.
+
+> You have to use Man or Google to know more about commands flags, in order to solve this exercise!
+> Google and Man will be your friends!
+
+### References
+
+- [tr](https://www.gnu.org/software/coreutils/tr).
+- [ls](https://www.gnu.org/software/coreutils/ls).
+- [sed](https://www.gnu.org/software/sed/manual/sed.html).