[doc] Add description, usage and notes to all modules

bumblebee/modules/dnf.py

@@ -6,6 +6,15 @@ import subprocess
 import bumblebee.module
 import bumblebee.util
 
+def usage():
+    return "dnf or dnf::<interval in seconds, defaults to 3600>"
+
+def notes():
+    return "Spawns a separate thread that invokes 'dnf updateinfo' every <interval> seconds. Critical status is if there is either more than 50 updates pending, or at least one of them is a security update."
+
+def description():
+    return "Checks DNF for updated packages and displays the number of <security>/<bugfixes>/<enhancements>/<other> pending updates."
+
 def get_dnf_info(obj):
     while True:
         try: