fix(0-shell) Add restrictions

subjects/0-shell/README.md

@@ -28,7 +28,7 @@ For this project you will only have to create a simple `Unix shell` where you ca
   - `mkdir`
   - `exit`
 
-> The commands need to be implemented from scratch. It is not allowed to execute external binaries.
+> The commands need to be implemented from scratch, without calling any external binaries and exclusively using low-level system calls directly, without relying on built-in functions or libraries that abstract file operations?
 
 - You must manage the program interruption `Ctrl + D`.
 - The project has to be written in a compiled language (like C, Rust, Go or other), **interpreted languages (like Perl and others) are not allowed**.

subjects/0-shell/audit/README.md

@@ -2,7 +2,7 @@
 
 ###### Was the project written in a compiled programming language?
 
-###### Are the commands mentioned in the subject implemented from scratch, without calling any external binaries?
+###### Are the commands mentioned in the subject implemented from scratch, without calling any external binaries and exclusively using low-level system calls directly, without relying on built-in functions or libraries that abstract file operations?
 
 #### Functional