Fixed a help text

owl.py

@@ -1536,7 +1536,7 @@ def cli_create_course(ident, name, teacher, token=None, semester=None):
 @click.argument("course_ident")
 @click.argument("teacher")
 def cli_add_teacher(course_ident, teacher):
-    """Add a teacher to an existing course. TEACHER is the teacher's full name."""
+    """Add a teacher to an existing course. TEACHER is the teacher's full name or e-mail."""
 
     teacher_user = cli_find_user(teacher)