docs: add F2F_APP env vars to .env.example

Author: JanR2024

.env.example

@@ -9,6 +9,12 @@ RTCV_SERVER=http://rtcv_key_ID_here:rtcv_key_here@localhost:4000
 # This can be set to a staging server so we don't have to run 2 instances of a scraper
 # RTCV_ALTERNATIVE_SERVER=http://rtcv_key_ID_here:rtcv_key_here@localhost:4000
 
+# Optional: route requests through the F2F App instead of directly to RT-CV
+# Uses f2f:// (http) or f2fs:// (https) protocol to distinguish from RTCV_SERVER basic auth
+# RTCV_SERVER is still required for incoming callback authentication
+# F2F_APP=f2fs://keyId:keySecret@app.first2find.nl
+# F2F_ALTERNATIVE_APP=f2fs://keyId:keySecret@app.first2find.nl
+
 # Set to true to skip the alive check that checks if the scraper is allowed to scrape.
 # This is useful for local development when a scraper is disabled on RT-CV.
 # DO NOT DEPLOY A SCRAPER WITH THIS ENABLED!