improve README with Usage and Prerequisites sections

README.md

@@ -1,6 +1,20 @@
 # sncf-smart-location
-Display train speed, maxspeed and name of current railway where your train (TGV or Intercités) is located.
+
+Display train speed, max speed and name of current railway where your train (TGV or Intercités) is located.
 
 Based on OpenStreetMap data, using Overpass-API
 
-You need to be connected to the Wi-Fi hostpost ( *_SNCF_WIFI_INTERCITES* or *_SNCF_WIFI_INOUI*)
+## Prerequisites
+
+You need to be connected to the Wi-Fi hotspot of your train (`_SNCF_WIFI_INTERCITES` or  `_SNCF_WIFI_INOUI`)  
+Make sure you have been authenticated through the `wifi.sncf` portal.
+
+## Usage
+
+Run with
+
+```
+$ bash sncf-smart-location.sh
+```
+
+