Add test for Format and update readme

QuickChartTest/QuickChartTest.cs

@@ -59,5 +59,32 @@ namespace QuickChartTest
             Assert.Contains("h=300", url);
             Assert.Contains("key=abc123", url);
         }
+
+        [Fact]
+        public void TestWithFormat()
+        {
+            Chart qc = new Chart
+            {
+                Width = 500,
+                Height = 300,
+                Format = "svg",
+                Config = @"{
+                type: 'bar',
+                data: {
+                    labels: ['Q1', 'Q2', 'Q3', 'Q4'],
+                    datasets: [{
+                        label: 'Users',
+                        data: [50, 60, 70, 180]
+                    }]
+                }
+            }"
+            };
+
+            string url = qc.GetUrl();
+            Assert.Contains("https://quickchart.io:443/chart", url);
+            Assert.Contains("w=500", url);
+            Assert.Contains("h=300", url);
+            Assert.Contains("f=svg", url);
+        }
     }
 }

README.md

@@ -77,6 +77,9 @@ The background color of the chart. Any valid HTML color works. Defaults to #ffff
 #### DevicePixelRatio: double
 The device pixel ratio of the chart. This will multiply the number of pixels by the value. This is usually used for retina displays. Defaults to 1.0.
 
+#### Format: string
+The output format of the chart. Defaults to "png"
+
 #### Key: string
 API key (not required)