docs(w&b): add fuel persistence feature (#565)

* docs(w&b): add fuel persistence feature

* add fuel persistence information

Author: Valastiri

docs/fbw-a32nx/feature-guides/loading-fuel-weight.md

@@ -18,7 +18,7 @@ Please select the correct version below.
 
 ---
 
-??? "General Fuel and Weight Information (Click to expand)"
+??? info "General Fuel and Weight Information (Click to expand)"
     ## General Fuel and Weight Information
 
     ### Operating Empty Weight
@@ -285,3 +285,34 @@ Get our [simBrief Profile](../installation.md#simbrief-airframe) for the Develop
     **NOTE:** Cargo will show only bag weight for 142 pax. Please ensure that you re-add any additional cargo that you may have been carrying originally.
 
     Press START to begin the process.
+
+---
+
+## Fuel Persistence
+
+!!! warning "Not Available in the Stable Version"
+
+After completing a flight the A32NX saves the amount of fuel on board to a special directory when at least one engine is off. This feature is tied to the aircraft registration 
+found in `atc_id` in the `acft.cfg`. 
+
+If you decide to exit the simulator after your flight, loading back in at a later time with the same livery and associated registration 
+will use the same amount of fuel from your previous flight.
+
+These files are saved in our Work folder under `AircraftStates` alongside other files we store. The work folder can be found using this guide - [here](../support/index.
+md#work-folder).
+
+!!! tip ""
+    Reminder: This file is created/updated **ONLY** on the ground and with at least an engine off.
+
+    If no registraiton is found the default value is ASX320.
+
+`AircraftStates/ASX320.ini` example:
+
+```ini title="ASX320.ini"
+[fuel]
+fuel_center_quantity = 0.000000
+fuel_left_quantity = 364.437298
+fuel_right_quantity = 343.734621
+fuel_left_aux_quantity = 228.000000
+fuel_right_aux_quantity = 228.000000
+```