improved graph appearance to be more clear

lib/pages/flood_station_page.dart

@@ -19,19 +19,17 @@ class FloodStationPage extends StatelessWidget {
           future: Api.fetchReadingsFromStation(_floodStation.id),
           builder: (context, snapshot) {
             if (snapshot.hasData) {
-              return ReadingGraph(
-                readings: snapshot.data!,
+              if (snapshot.data!.isEmpty) {
+                return Text('No readings on record.');
+              }
+              return Center(
+                child: Padding(
+                  padding: const EdgeInsets.fromLTRB(20, 0, 20, 20),
+                  child: ReadingGraph(
+                    readings: snapshot.data!,
+                  ),
+                ),
               );
-
-              // return ListView.builder(
-              //   itemBuilder: (context, index) {
-              //     return ListTile(
-              //       title:
-              //           Text(snapshot.data!.elementAt(index).value.toString()),
-              //     );
-              //   },
-              //   itemCount: snapshot.data!.length,
-              // );
             } else {
               return Placeholder();
             }