Documentation for yessssms component (#3801)

* Documentation for yessssms component

* typo

* updated documentation for YesssSMS

* Remove line breaks

source/_components/notify.yessssms.markdown

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+---
+layout: page
+title: "Yesss SMS"
+description: "Instructions how to add user notifications to Home Assistant."
+date: 2017-10-27 16:00
+sidebar: true
+comments: false
+sharing: true
+footer: true
+logo: yesssat.png
+ha_category: Notifications
+ha_release: 0.57
+---
+
+The `yessssms` platform is using the Austrian mobile operator [Yesss.at](https://yesss.at) to send SMS via its web-site.
+
+<p class='note warning'>
+Regular charges apply and a contract or prepaid plan is needed.
+</p>
+
+<p class='note warning'>
+Do not use this for high frequency notifications. The web-SMS page is rate limited and sending more than 45 SMS/h might get you blocked.
+</p>
+
+You can send to any number, but your phone number will appear as sender.
+
+To enable SMS notifications in your installation, add the following to your `configuration.yaml` file:
+
+```yaml
+# Example configuration.yaml entry
+notify:
+  - name: NOTIFIER_NAME
+    platform: yessssms
+    username: YOUR_PHONE_NUMBER
+    password: YOUR_PASSWORD
+    recipient: PHONE_NUMBER_TO_NOTIFY
+```
+
+Configuration variables:
+
+- **username** (*Required*): This is your login name (usually your phone number). Veryfy that you can use your credentials on the Yesss.at website.
+- **password** (*Required*): This is the password you use to login to Yesss.at.
+- **recipient** (*Required*): This is the phone number you want to send the SMS notification to.
+
+<p class='note warning'>
+Verify that your credentials work on [Yesss.at's website](https://yesss.at). Using the wrong credentials three times in a row will get you blocked for one hour.
+</p>