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_en.h

@@ -204,6 +204,8 @@ static const char* const I18N_EN[] = {
 
     "Weather",
     "The weather icon shows the current weather for your active location. If a location preset is selected, its weather is shown instead.",
+
+    "Tip: at itilog.com (https://www.itilog.com/) you can enter your address for free and instantly get its exact coordinates. It's worth it - automatic IP-based location can easily be off by 20-30 km, so you might hear a plane overhead while the radar stays empty. With the exact coordinates entered as a preset, the proximity LED really does blink in sync with the aircraft above you.",
 };
 
 static_assert(sizeof(I18N_EN) / sizeof(I18N_EN[0]) == (size_t)StringId::COUNT,