add note about personas (#1196)

Author: sanscontext

src/guides/usage-and-billing/mtus-and-throughput.md

@@ -90,15 +90,14 @@ Blocked events (sometimes called "violations") only count toward your MTU limit
 
 If you enable violation forwarding, it generates one (1) additional MTU in your workspace, total. If you are on an API billing plan, you are charged for the increased API volume generated by the forwarded violations. Forwarded violations might also generate costs in downstream destinations and data warehouses connected to the violations source.
 
-<!-- TODO
+
 ## MTUs and Personas
 
 > success ""
-> Personas is a Business Tier feature. If you are on a Free or Team plan, this section does not apply to you.
+> [Personas](/docs/personas/) is a Business Tier feature. If you are on a Free or Team plan this section does not apply to you (because you do not have this feature).
+
+All Personas data are omitted from billing MTU and API throughput calculations, including [computed traits](/docs/personas/computed-traits/), [SQL traits](/docs/personas/sql-traits/), and [audiences](/docs/personas/audiences/).
 
-- Personas volume does not count against your MTU limit.
-- Does it do anything to your throughput limit? API calls?
--->
 
 ## MTUs and Replays