pylintrc: document deprecated-modules field

BUG=None
TEST=cros lint still works

Change-Id: Ic46aeb78d6d0a5a5b156a48514cb50c4c7e83094
Reviewed-on: https://chromium-review.googlesource.com/1179993
Commit-Ready: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Alex Klein <saklein@chromium.org>
diff --git a/pylintrc b/pylintrc
index 5970352..14e54bb 100644
--- a/pylintrc
+++ b/pylintrc
@@ -285,8 +285,18 @@
 
 [IMPORTS]
 
-# Deprecated modules which should not be used, separated by a comma
-deprecated-modules=regsub,TERMIOS,Bastion,rexec,optparse
+# Deprecated modules which should not be used, separated by a comma.
+# Bastion: Dropped in Python 3.
+# optparse: Use the 'argparse' module instead.
+# regsub: Use the 're' module instead.
+# rexec: Dropped in Python 3.
+# TERMIOS: Use the 'termios' module instead.
+deprecated-modules=
+    Bastion,
+    optparse,
+    regsub,
+    rexec,
+    TERMIOS,
 
 # Create a graph of every (i.e. internal and external) dependencies in the
 # given file (report RP0402 must not be disabled)