Ensure that lint S014 has a proper test. (cylc#6324)

cylc/flow/scripts/lint.py

@@ -195,6 +195,15 @@ def get_wallclock_directives():
 def check_wallclock_directives(line: str) -> Union[Dict[str, str], bool]:
     """Check for job runner specific directives
     equivelent to exection time limit.
+
+    It's recommended that users prefer execution time limit
+    because it gives the Cylc scheduler awareness should communications
+    with a remote job runner be lost.
+
+    Examples:
+        >>> this = check_wallclock_directives
+        >>> this('    -W 42:22')
+        {'directive': '-W 42:22'}
     """
     for directive in set(WALLCLOCK_DIRECTIVES.values()):
         if line.strip().startswith(directive):