Startup.cs

using System.IO;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.PlatformAbstractions;
using Swashbuckle.Swagger.Model;

namespace TesteAPIREST
{
    public class Startup
    {
        public Startup(IHostingEnvironment env)
        {
            var builder = new ConfigurationBuilder()
                .SetBasePath(env.ContentRootPath)
                .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
                .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true)
                .AddEnvironmentVariables();
            Configuration = builder.Build();
        }

        public IConfigurationRoot Configuration { get; }

        public void ConfigureServices(IServiceCollection services)
        {
            services.AddMvc();

            // Configurando o serviço de documentação do Swagger
            services.AddSwaggerGen();

            services.ConfigureSwaggerGen(options =>
            {
                options.SingleApiVersion(new Info
                {
                    Version = "v1",
                    Title = "Conversor de Alturas",
                    Description = "Exemplo de API REST criada com o ASP.NET Core",
                    Contact = new Contact { Name = "Renato Groffe", Url = "http://renatogroffe.net" }
                });

                string caminhoAplicacao =
                    PlatformServices.Default.Application.ApplicationBasePath;
                string nomeAplicacao =
                    PlatformServices.Default.Application.ApplicationName;
                string caminhoXmlDoc =
                    Path.Combine(caminhoAplicacao, $"{nomeAplicacao}.xml");

                options.IncludeXmlComments(caminhoXmlDoc);
            });
        }

        public void Configure(
            IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
        {
            loggerFactory.AddConsole(Configuration.GetSection("Logging"));
            loggerFactory.AddDebug();

            app.UseMvc();
            app.UseMvcWithDefaultRoute();

            // Ativando middlewares para uso do Swagger
            app.UseSwagger();
            app.UseSwaggerUi();
        }
    }
}