Update README.md

Author: nejcskofic

README.md

@@ -11,8 +11,11 @@ This is why this library consists of simple interfaces for object mapping contra
 
 ## Usage
 
-Install NuGet package to your project - you can find current release [here](https://www.nuget.org/packages/SimpleObjectMapper/). This will add ObjectMapper.Framework to your references and diagnostic analyser under analyzers node.
-You can then use mapper interfaces from ObjectMapper.Framework assembly to define mapping. For example let's define two classes with some matching properties:
+Install NuGet package to your project - you can find current release [here](https://www.nuget.org/packages/SimpleObjectMapper/). This will add ObjectMapper.Framework to your references and diagnostic analyser under analyzers node. You can then use mapper interfaces or attribute from ObjectMapper.Framework assembly to define mapping. 
+
+### IObjectMapper<T> interface
+
+Let's define two classes with some matching properties:
 
 ```C#
 using ObjectMapper.Framework;
@@ -42,7 +45,7 @@ namespace TestClassLibrary
 }
 ```
 
-Let's say that we want to define mapping from class ClassA to ClassB. We specify that ClassA implements IObjectMapper<ClassB> interface. If we have cursor on IObjectMapper<ClassB> symbol, Visual Studio will display lightbulb on the right side. By clicking on lightbulb (or using space + . shortcut), you will get menu of options. If you click 'Generate implementation' interface implementation with mapping code will be generated for you. For the above example result is as follows:
+Let's say that we want to define mapping from class ClassA to ClassB. We specify that ClassA implements IObjectMapper<ClassB> interface. If we have caret on IObjectMapper<ClassB> symbol, Visual Studio will display lightbulb on the right side. By clicking on lightbulb (or using left control + . shortcut), you will get menu of options. If you click 'Generate implementation' interface implementation with mapping code will be generated for you. For the above example result is as follows:
 
 ```C#
 using ObjectMapper.Framework;
@@ -80,8 +83,56 @@ namespace TestClassLibrary
 }
 ```
 
+If you have method already defined (or generated), you can set caret on method name and 'Generate implementation' action will be available.
+
+### IObjectMapperAdapter<T, U> interface
+
 If you do not want to have mapping code inside your POCO classes you can use IObjectMapperAdapter<T,U>. By having cursor on IObjectMapperAdapter symbol, you can invoke 'Generate implementation' and generator will generate mapping code for mapping from class T to class U and from class U to class T.
 
+If we take previous example of ClassA and ClassB and we define new class Adapter which implements IObjectMapperAdapter<ClassA, ClassB> generated code for Adapter class is as follows:
+
+```C#
+public class Adapter : IObjectMapperAdapter<ClassA, ClassB>
+{
+    public void MapObject(ClassA source, ClassB target)
+    {
+        target.Prop1 = source.Prop1 ?? default(int);
+        target.Prop2 = source.Prop2;
+        target.Prop3 = source.Prop3;
+        target.Prop4.CopyFrom(source.Prop4);
+    }
+
+    public void MapObject(ClassB source, ClassA target)
+    {
+        target.Prop1 = source.Prop1;
+        target.Prop2 = source.Prop2;
+        target.Prop3 = source.Prop3;
+        target.Prop4.CopyFrom(source.Prop4);
+    }
+}
+```
+
+### ObjectMapperMethodAttribute attribute
+
+If you want to have ad hoc method for mapping without actually implementing one of the above interfaces, you can annotate mapping method with ObjectMapperMethodAttribute attribute. This attribute can be applied only to methods with following signatures:
+- Method accepts exactly two parameters
+- Method return type is void
+
+Compile time error will be raised otherwise. If you then place caret on method name, lightbulb will apear and 'Generate implementation' action will be available.
+
+Example of method with applied attribute:
+
+```C#
+[ObjectMapperMethod]
+private static void MapFromAToB(ClassA source, ClassB target)
+{
+    target.Prop1 = source.Prop1 ?? default(int);
+    target.Prop2 = source.Prop2;
+    target.Prop3 = source.Prop3;
+    target.Prop4.CopyFrom(source.Prop4);
+}
+```
+
 ## Code generation rules
 
 1. Property names must match in both classes.