Add day selector

Days/Day2.cs

@@ -0,0 +1,14 @@
+using Spectre.Console;
+
+namespace AdventOfCode.Days;
+
+public class Day2 : Day
+{
+    public override int Number { get; } = 2;
+    public override string Name { get; } = "Second day";
+    
+    public override void Run()
+    {
+        AnsiConsole.WriteLine("Day 2 result");
+    }
+}