Add AdvertiseCommand example to docs

docs_test.go

@@ -0,0 +1,20 @@
+package keybase
+
+func ExampleKeybase_AdvertiseCommand() {
+	var k = NewKeybase()
+
+	// Clear out any previously advertised commands
+	k.ClearCommands()
+
+	// Create BotAdvertisement
+	c := BotAdvertisement{
+		Type: "public",
+		BotCommands: []BotCommand{
+			NewBotCommand("help", "Get help using this bot"),
+			NewBotCommand("hello", "Say hello"),
+		},
+	}
+
+	// Send advertisement
+	k.AdvertiseCommand(c)
+}