Added info C# null-propagation

Another tool I found useful when learning C#

csharp.html.markdown

@@ -444,6 +444,9 @@ on a new line! ""Wow!"", the masses cried";
             // in case variable is null
             int notNullable = nullable ?? 0; // 0
             
+            // ?. is an operator for null-propogation - a shorthand way of checking for null
+            nullable?.Print(); // Use the Print() extension method if nullable isn't null
+
             // IMPLICITLY TYPED VARIABLES - you can let the compiler work out what the type is:
             var magic = "magic is a string, at compile time, so you still get type safety";
             // magic = 9; will not work as magic is a string, not an int