Create Behaviors README

Behaviors/README.md

@@ -0,0 +1,73 @@
+# Port Xamarin.Forms Behaviors to .NET MAUI
+
+Behaviors let you add functionality to user interface controls without having to subclass them. Instead, the functionality is implemented in a behavior class and attached to the control as if it was part of the control itself.
+
+In .NET MAUI the same concept works exactly the same, being able to reuse all the code. 
+
+Let's see an example.
+
+Xamarin.Forms
+
+```
+using Xamarin.Forms;
+
+namespace Behaviors
+{
+    public class NumericValidationBehavior : Behavior<Entry>
+    {
+        protected override void OnAttachedTo(Entry entry)
+        {
+            entry.TextChanged += OnEntryTextChanged;
+            base.OnAttachedTo(entry);
+        }
+
+        protected override void OnDetachingFrom(Entry entry)
+        {
+            entry.TextChanged -= OnEntryTextChanged;
+            base.OnDetachingFrom(entry);
+        }
+
+        void OnEntryTextChanged(object sender, TextChangedEventArgs args)
+        {
+            bool isValid = double.TryParse(args.NewTextValue, out double result);
+            ((Entry)sender).TextColor = isValid ? Color.Default : Color.Red;
+        }
+    }
+}
+```
+.NET MAUI
+
+```
+using Microsoft.Maui.Controls;
+using Microsoft.Maui.Graphics;
+
+namespace Behaviors
+{
+    public class NumericValidationBehavior : Behavior<Entry>
+    {
+        protected override void OnAttachedTo(Entry entry)
+        {
+            entry.TextChanged += OnEntryTextChanged;
+            base.OnAttachedTo(entry);
+        }
+
+        protected override void OnDetachingFrom(Entry entry)
+        {
+            entry.TextChanged -= OnEntryTextChanged;
+            base.OnDetachingFrom(entry);
+        }
+
+        void OnEntryTextChanged(object sender, TextChangedEventArgs args)
+        {
+            bool isValid = double.TryParse(args.NewTextValue, out double result);
+            ((Entry)sender).TextColor = isValid ? Colors.Black : Colors.Red;
+        }
+    }
+}
+```
+
+_What is the difference?_. The code is exactly the same except for one detail, namespaces.
+
+Xamarin.Forms namespace changes to **Microsoft.Maui.Controls **namespace. 
+
+On the other hand, all the basic types such as: Color, Rectangle or Point have become available in **Microsoft.Maui.Graphics**. For that reason, and because using colors in this Behavior we also need this new namespace.