Clarify instructions for the exercise `boolean`

subjects/boolean/README.md

@@ -2,14 +2,12 @@
 
 ### Instructions
 
-Create a `.go` file.
+Create a new directory called `boolean`.
 
-- The code below has to be copied in that file.
+- The code below has to be copied in a file called `main.go` inside the `boolean` directory.
 
 - The necessary changes have to be applied so that the program works.
 
-- The program must be submitted inside a folder with the name `boolean`.
-
 ### Code to be copied
 
 ```go