docs: fix incorrect env name

Author: alexluong

docs/pages/features/tenant-user-portal.mdx

@@ -20,7 +20,7 @@ The portal is a React SPA that is distributed via the API.
 
 `PORTAL_REFERER_URL` is used to redirect the user when the JWT token is expired or when the user clicks "back".
 
-`ORGANIZATION_NAME` is used to display the name of the organization deploying the portal.
+`PORTAL_ORGANIZATION_NAME` is used to display the name of the organization deploying the portal.
 
 ## Theming