Add cmdlet example project with readme

docs/cmdlet-example/SendGreeting.cs

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+// Example from https://msdn.microsoft.com/en-us/library/dd901838(v=vs.85).aspx
+
+using System.Management.Automation;  // Windows PowerShell assembly.
+
+namespace SendGreeting
+{
+    // Declare the class as a cmdlet and specify and
+    // appropriate verb and noun for the cmdlet name.
+    [Cmdlet(VerbsCommunications.Send, "Greeting")]
+    public class SendGreetingCommand : Cmdlet
+    {
+        // Declare the parameters for the cmdlet.
+        [Parameter(Mandatory=true)]
+        public string Name
+        {
+            get { return name; }
+            set { name = value; }
+        }
+        private string name;
+
+        // Overide the ProcessRecord method to process
+        // the supplied user name and write out a
+        // greeting to the user by calling the WriteObject
+        // method.
+        protected override void ProcessRecord()
+        {
+            WriteObject("Hello " + name + "!");
+        }
+    }
+}