add basic skeleton for AoC 2020

2020/AdventOfCode.csproj

@@ -0,0 +1,8 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net5.0</TargetFramework>
+  </PropertyGroup>
+
+</Project>

2020/Program.cs

@@ -0,0 +1,9 @@
+using System;
+
+namespace AdventOfCode {
+  class Program {
+    static void Main(string[] args) {
+      Console.WriteLine("Hello World!");
+    }
+  }
+}