Add comment to kathjax.py to update references

Summary: I'm not sure if this is the right place to check this in, so let me know if there's a better place.

Test Plan: None, it's a comment.

Reviewers: alex

CC: alpert

Differential Revision: http://phabricator.khanacademy.org/D5213
Update comment
Merge branch 'add_comment'