Adjust message about offline database migration (#21460)

Tweak message about offline database migration

src/layouts/ha-init-page.ts

@@ -39,7 +39,13 @@ class HaInitPage extends LitElement {
           </div>
           <div id="loading-text">
             ${this.migration
-              ? "Database migration in progress, please wait this might take some time"
+              ? html`
+                  Database upgrade is in progress, Home Assistant will not start
+                  until the upgrade is completed.
+                  <br /><br />
+                  The upgrade may need a long time to complete, please be
+                  patient.
+                `
               : "Loading data"}
           </div>
         `;