Added covid-19 example app and Updated the readme (#73)

covid19_mobile_app/lib/widgets/graph.dart

@@ -0,0 +1,51 @@
+import 'package:flutter/material.dart';
+import 'package:bezier_chart/bezier_chart.dart';
+
+// Widget that will build the graph
+Widget buildGraph(
+    BuildContext context, List<Map<String, dynamic>> datesAndValues) {
+  // Data is avalaible from a particular date and we are getting that here
+  final fromDate = datesAndValues[0]['date'];
+
+  // Data is avalaible until a particular date and we are getting that here
+  final toDate = datesAndValues.last['date'];
+
+  // Add dates and values corresponding to those dates
+  // in a list
+  List<DataPoint<DateTime>> dataPoints = [];
+  for (final dateAndValue in datesAndValues) {
+    dataPoints.add(DataPoint<DateTime>(
+        value: double.parse(dateAndValue['value'].toString()),
+        xAxis: dateAndValue['date']));
+  }
+
+  return Center(
+    child: Container(
+      decoration: BoxDecoration(
+        color: Colors.red,
+      ),
+      height: MediaQuery.of(context).size.height / 2,
+      width: MediaQuery.of(context).size.width,
+      child: BezierChart(
+        fromDate: fromDate,
+        bezierChartScale: BezierChartScale.WEEKLY,
+        toDate: toDate,
+        selectedDate: toDate,
+        series: [
+          BezierLine(
+            data: dataPoints,
+          ),
+        ],
+        config: BezierChartConfig(
+          physics: BouncingScrollPhysics(),
+          verticalIndicatorStrokeWidth: 3.0,
+          verticalIndicatorColor: Colors.black26,
+          showVerticalIndicator: true,
+          verticalIndicatorFixedPosition: false,
+          backgroundColor: Colors.transparent,
+          footerHeight: 30.0,
+        ),
+      ),
+    ),
+  );
+}