Add example and documentation

example/main.dart

@@ -0,0 +1,5 @@
+import 'package:db_construction_site/db_construction_site.dart';
+
+void main() {
+  DBConstructionSite().connections.findConnections(Region.hesse);
+}

lib/db_construction_site.dart

@@ -5,6 +5,7 @@ import 'src/services/connection_service.dart';
 export 'src/models/index.dart';
 
 class DBConstructionSite {
+  /// Find train routes and connections that are affected by construction sites
   final ConnectionService connections;
 
   DBConstructionSite({baseUrl = 'https://bauinfos.deutschebahn.com/app'})