Improve subjects for ztail and pilot

subjects/pilot.en.md

@@ -4,6 +4,12 @@
 
 Write a `go` file so that the following program compiles.
 
+### Note:
+
+- The code bellow must be submitted.
+
+- Be careful with the expected files.
+
 ### Usage
 
 ```go

subjects/ztail.en.md

@@ -10,4 +10,10 @@ Write a program called `ztail` that has the same behaviour as the system command
 
 -   For the program to pass the tests the convention for the return code of program in Unix systems should be followed (see os.Exit).
 
+-   Handle the errors and output the same error messages as `tail`.
+
 -   For more information consult the man page for `tail`.
+
+### Note:
+
+This program is gonna be tested against `tail`, be sure to check all the different error messages with different permutations of the arguments.