Add itilog.com coordinate tip to location presets info screen and README

Adds a new info paragraph to the Location Presets "?" screen (all 6
languages) recommending itilog.com for getting exact address
coordinates, since automatic IP-based geolocation can easily be off by
20-30 km - enough to hear a plane while the radar stays empty. Adds
the same tip to the README's Getting Started section, with a
clickable link.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/i18n.h

@@ -221,6 +221,12 @@ enum class StringId : uint8_t {
     WEATHER_INFO_TITLE,
     WEATHER_INFO_BODY,
 
+    // Zusaetzlicher Info-Absatz im Standort-Presets-Screen (Menue >
+    // Flugoptionen > Standort-Presets > "?") mit Tipp zu itilog.com fuer
+    // exakte Koordinaten - deutlich genauer als die automatische
+    // IP-Standortbestimmung (die leicht 20-30km danebenliegen kann).
+    LOCATION_INFO_PARA6,
+
     COUNT
 };