Add Plaid and SimpleFIN env var stubs to .env.example

Both commented out — uncomment and fill in when ready to wire up
US bank automation.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.env.example

@@ -50,3 +50,13 @@ FIREFLY_III_ACCESS_TOKEN=REPLACE_AFTER_FIRST_RUN
 # --- Cron ---
 # Generate with: python3 -c "import secrets; print(secrets.token_hex(16))"
 STATIC_CRON_TOKEN=REPLACE_WITH_RANDOM_HEX
+
+# --- Plaid (optional — full automation, US banks) ---
+# Requires approved Plaid account: https://plaid.com
+# PLAID_CLIENT_ID=
+# PLAID_SECRET=
+# PLAID_ENV=sandbox     # sandbox | development | production
+
+# --- SimpleFIN Bridge (optional — simpler US bank automation, ~$1.50/mo) ---
+# Connect accounts at https://bridge.simplefin.org, then paste the access URL below
+# SIMPLEFIN_URL=