Clarify shell command execution instructions in course-definition.yml

Update the description to specify that the shell should handle command searches and permissions. This change enhances clarity by consistently referring to the shell's role in executing commands and improves user understanding of command handling outcomes.

Author: andy1li

course-definition.yml

@@ -312,15 +312,15 @@ stages:
     description_md: |-
       In this stage, you'll extend the `type` builtin to search for executable files using [PATH](https://en.wikipedia.org/wiki/PATH_(variable)).
 
-      [PATH](https://en.wikipedia.org/wiki/PATH_(variable)) is an environment variable that specifies a set of directories where executable programs are located. When a command is received, the program should search for the command in the directories listed in the PATH environment variable.
+      [PATH](https://en.wikipedia.org/wiki/PATH_(variable)) is an environment variable that specifies a set of directories where executable programs are located. When a command is received, your shell should search for the command in the directories listed in the PATH environment variable.
 
-      For example, PATH like `/dir1:/dir2:/dir3` means that the program should search for the command in `/dir1`, then `/dir2`, and finally `/dir3`, in that order.
+      For example, PATH like `/dir1:/dir2:/dir3` means that your shell should search in `/dir1`, then `/dir2`, and finally `/dir3`, in that order.
 
       Caveat: Not all commands found are necessarily executable.
 
-      - If the command is found (but it does not have execute permissions), the program should skip it and continue searching. 
-      - If the command is found (and it has execute permissions), the program should print the path to the command. 
-      - If the command is not found, the program should print `<command>: not found`.
+      - If the command is found (but it does not have execute permissions), your shell should skip it and continue searching. 
+      - If the command is found (and it has execute permissions), your shell should print the path to the command. 
+      - If the command is not found, your shell should print `<command>: not found`.
 
       ### Tests