Add alert about yesterday train feature

sw.js

@@ -1,4 +1,4 @@
-const VERSION = 'v11'
+const VERSION = 'v12'
 const API_ORIGIN = 'https://scraper.infotren.dcdev.ro/'
 const API_TRAINS = `${API_ORIGIN}v3/trains`
 const API_STATIONS = `${API_ORIGIN}v3/stations`
@@ -49,7 +49,7 @@ self.addEventListener('install', (event) => {
   )
 })
 
-const deleteCache = (key) => caches.delete(key)
+const deleteCache = (/** @type {string} */ key) => caches.delete(key)
 
 const deleteOldCaches = async () => {
    const cacheKeepList = [VERSION]

view-train.js

@@ -489,4 +489,9 @@ window.addEventListener('load', function (e) {
 			})
 		}
 	}, 500)
+
+	if (this.localStorage && !this.localStorage.getItem('info-yesterday')) {
+		this.alert("New feature: You can now view yesterday's train by selecting the date!")
+		this.localStorage.setItem('info-yesterday', 'true')
+	}
 })