Added new getting started guide

Thanks @MinnDevelopment for his awesome work on
the JDA guide that had no influence here at all.

docs/guides/samples/intro/async-context.cs

@@ -0,0 +1,15 @@
+using System;
+using System.Threading.Tasks;
+
+namespace MyBot
+{
+	public class Program
+	{
+		public static void Main(string[] args)
+			=> new Program().MainAsync().GetAwaiter().GetResult();
+
+		public async Task MainAsync()
+		{
+		}
+	}
+}