Update readme with an example to use gem in app

README.md

@@ -6,18 +6,26 @@ calculators.
 
 ## Usage
 
-Install the gem :
+Install the gem:
 
-    $ gem install chronopost_fuel_multiplier
+    $ gem install chronopost_fuel_adjustment_coefficients
 
-Run the gem :
+Run the gem:
 
-    $ chronopost_fuel_multiplier
+    $ chronopost_fuel_adjustment_coefficients
 
-Get the result :
+Get the result:
 
     # Fuel multipliers for 'Février 2017'
     # Fetched from http://www.chronopost.fr/fr/surcharge-carburant
 
     AIR_FUEL_MULTIPLIER  = 1.1685
     ROAD_FUEL_MULTIPLIER = 1.1150
+
+Or use it in your app:
+
+    require 'chronopost_fuel_adjustment_coefficients'
+
+    ch = ChronopostFuelAdjustmentCoefficients.new
+    ch.road_multiplier      # 0.11685e1
+    ch.air_multiplier       # 0.1115e1