Add sample bots to the solution (#972)

* Add sample bots to the solution

* Fix missing attributes, show use of preconditions

samples/01_basic_ping_bot/Program.cs

@@ -0,0 +1,69 @@
+using System;
+using System.Threading.Tasks;
+using Discord;
+using Discord.WebSocket;
+
+namespace _01_basic_ping_bot
+{
+    // This is a minimal, barebones example of using Discord.Net
+    //
+    // If writing a bot with commands, we recommend using the Discord.Net.Commands
+    // framework, rather than handling commands yourself, like we do in this sample.
+    //
+    // You can find samples of using the command framework:
+    // - Here, under the 02_commands_framework sample
+    // - https://github.com/foxbot/DiscordBotBase - a barebones bot template
+    // - https://github.com/foxbot/patek - a more feature-filled bot, utilizing more aspects of the library
+    class Program
+    {
+        private DiscordSocketClient _client;
+
+        // Discord.Net heavily utilizes TAP for async, so we create
+        // an asynchronous context from the beginning.
+        static void Main(string[] args)
+            => new Program().MainAsync().GetAwaiter().GetResult();
+
+        public async Task MainAsync()
+        {
+            _client = new DiscordSocketClient();
+
+            _client.Log += LogAsync;
+            _client.Ready += ReadyAsync;
+            _client.MessageReceived += MessageReceivedAsync;
+
+            // Tokens should be considered secret data, and never hard-coded.
+            await _client.LoginAsync(TokenType.Bot, Environment.GetEnvironmentVariable("token"));
+            await _client.StartAsync();
+
+            // Block the program until it is closed.
+            await Task.Delay(-1);
+        }
+
+        private Task LogAsync(LogMessage log)
+        {
+            Console.WriteLine(log.ToString());
+            return Task.CompletedTask;
+        }
+
+        // The Ready event indicates that the client has opened a
+        // connection and it is now safe to access the cache.
+        private Task ReadyAsync()
+        {
+            Console.WriteLine($"{_client.CurrentUser} is connected!");
+
+            return Task.CompletedTask;
+        }
+
+        // This is not the recommmended way to write a bot - consider
+        // reading over the Commands Framework sample.
+        private async Task MessageReceivedAsync(SocketMessage message)
+        {
+            // The bot should never respond to itself.
+            if (message.Author.Id == _client.CurrentUser.Id)
+                return;
+
+            if (message.Content == "!ping")
+                await message.Channel.SendMessageAsync("pong!");
+        }
+    }
+}