Update apps.html

Added a link to the Filter Settings page to make sure users know what parameters must be used when updating filters.
Merge branch 'patch-2' of github.com:jaysonsperling/docs into jaysonsperling-patch-2
move note to info block
change href to relative
Merge pull request #257 from sendgrid/jaysonsperling-patch-2

Update subuser apps API reference with a note re: filter settings