Add tts.baidu platform (#4032)

* Add tts.baidu platform

* Update tts.baidu.markdown

Change appid to api_id, apikey to api_key, and secretkey to secret_key, because the baidu.py platform program changed.

source/_components/tts.baidu.markdown

@@ -0,0 +1,38 @@
+---
+layout: page
+title: "Baidu Text-to-Speech"
+description: "Instructions how to setup Baidu TTS with Home Assistant."
+date: 2017-11-21 09:00
+sidebar: true
+comments: false
+sharing: true
+footer: true
+logo: baiducloud.png
+ha_category: Text-to-speech
+ha_release: 0.59
+---
+
+The `baidu` text-to-speech platform uses [Baidu TTS engine](https://cloud.baidu.com/product/speech/tts) to read a text with natural sounding voices.
+
+To get started, add the following lines to your `configuration.yaml`:
+
+```yaml
+#Example configuration.yaml entry
+tts:
+  - platform: baidu
+    app_id: YOUR_APPID
+    api_key: YOUR_APIKEY
+    secret_key: YOUR_SECRETKEY
+    person: 4
+```
+
+Configuration variables:
+
+- **app_id** (*Required*): AppID for use this service, registered on Baidu.
+- **api_key** (*Required*): Apikey from Baidu.
+- **secret_key** (*Required*): Secretkey from Baidu.
+- **speed** (*Optional*): Audio speed, from 0 to 9, default is 5.
+- **pitch** (*Optional*): Audio pitch, from 0 to 9, default is 5.
+- **volume** (*Optional*): Audio volume, from 0 to 15, default is 5.
+- **person** (*Optional*): You can choose 0, 1, 3, 4, default is 0(a female voice).
+