WIP: Documentation: add Hello World and How to add it to Giraffe

[0x53A]

closes https://github.com/SaturnFramework/Saturn/issues/243

[0x53A]

One more thing I might add is a side by side comparison between Saturn and C# MVC Controllers.

If you create a new ASP.NET Core app and choose API

it creates a WeatherForecastController:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Logging;

namespace WebApplication1.Controllers
{
    [ApiController]
    [Route("[controller]")]
    public class WeatherForecastController : ControllerBase
    {
        private static readonly string[] Summaries = new[]
        {
            "Freezing", "Bracing", "Chilly", "Cool", "Mild", "Warm", "Balmy", "Hot", "Sweltering", "Scorching"
        };

        private readonly ILogger<WeatherForecastController> _logger;

        public WeatherForecastController(ILogger<WeatherForecastController> logger)
        {
            _logger = logger;
        }

        [HttpGet]
        public IEnumerable<WeatherForecast> Get()
        {
            var rng = new Random();
            return Enumerable.Range(1, 5).Select(index => new WeatherForecast
            {
                Date = DateTime.Now.AddDays(index),
                TemperatureC = rng.Next(-20, 55),
                Summary = Summaries[rng.Next(Summaries.Length)]
            })
            .ToArray();
        }
    }
}

The plan is to translate that to Saturn.

[Krzysztof-Cieslak]

@0x53A, thanks a lot for this PR! ❤️

[0x53A]

Haha thanks for merging it, I started it and then ... forgot about it again