Add sponsoredFPC concept stub

docs/docs/developers/guides/js_apps/pay_fees.md

@@ -21,6 +21,11 @@ Processing this transaction first claims bridged fee juice then is paid for from
 
 A fee paying contract (FPC) is created and nominates a token that it accepts to then pay for txs in fee juice. So a user doesn't need to hold fee juice, they only need the token that the FPC accepts.
 
+### Sponsored Fee Paying Contract
+
+A contract that will pay for a number of transactions without requiring payment. Which is helpful for bootstrapping development.
+
+
 ## Fee Options
 
 Functions pertaining to sending a transaction, such as `deploy` and `send`, each include a `fee` variable defined with the following (optional) parameters: