Add documentation for Preconditions, Aliases, Command Structure

Resolves #223

docs/guides/samples/groups.cs

@@ -0,0 +1,15 @@
+[Module("admin")]
+public class AdminModule
+{
+    [Group("mod")]
+    public class ModerationGroup
+    {
+        // ~admin mod ban foxbot#0282
+        [Command("ban")]
+        public async Task Ban(IMessage msg, IGuildUser user) { }
+    }
+
+    // ~admin clean 100
+    [Command("clean")]
+    public async Task Clean(IMessage msg, int count = 100) { }
+}