Update legend.rst

Update documentation on legends

Author: sharonchoong

models/legend.rst

@@ -3,3 +3,46 @@ Legend
 ======
 
 .. note:: This section is under construction. Please contribute!
+
+Overview
+--------
+
+For a legend to appear, the ``Series.Title`` property must be set.  
+
+Basic Options
+-------------
+Legend options are specified in the ``PlotModel``.
+
+1. LegendPlacement
+  * Place the legends inside/outside the plot area
+2. LegendPosition
+  * Place the legend box in the top/middle/bottom left/center/right corner
+3. LegendOrientation
+  * Orient the items horizontally/vertically
+4. LegendBackground
+  * Gets or sets the background color of the legend. Defaults to no background
+5. LegendFontSize
+  * Set the size of the legend font
+6. LegendMaxWidth
+  * Set the max width of the legend
+7. LegendMaxHeight
+  * Set the max height of the legend
+8. IsLegendVisible
+  * Show/hide the legend. If the ``Title``s of the chart's series are properly set, defaults to showing the legend.
+  
+Example
+-------
+
+.. code:: csharp
+
+    var model = new PlotModel();
+    model.LegendPosition = LegendPosition.BottomCenter;
+    model.LegendPlacement = LegendPlacement.Outside;
+    model.LegendOrientation = LegendOrientation.Horizontal;
+                
+    var lineSeries = new LineSeries()
+    { 
+      Title = "MyTitle", //this is required for legends
+      ItemsSource = dataPoints
+    }
+    model.Series.Add(lineSeries);