Improve video helper documentation

test/_posts/2017-01-23-layout-header-video.md

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+---
+title: "Layout: Header Video"
+header:
+  video:
+    id: XsxDH4HcOWA
+    provider: youtube
+categories:
+  - Layout
+  - Uncategorized
+tags:
+  - video
+  - layout
+---
+
+This post should display a **header with a responsive video**, if the theme supports it.
+
+## Settings
+
+| Parameter  | Required     | Description |
+|----------  |---------     | ----------- |
+| `id`       | **Required** | ID of the video |
+| `provider` | **Required** | Hosting provider of the video, either `youtube` or `vimeo` |
+
+### YouTube
+
+To embed the following YouTube video at url `https://www.youtube.com/watch?v=XsxDH4HcOWA` (long version) or `https://youtu.be/XsxDH4HcOWA` (short version) into a post or page's main content you'd use: 
+
+```liquid
+{% raw %}{% include video id="XsxDH4HcOWA" provider="youtube" %}{% endraw %}
+```
+
+{% include video id="XsxDH4HcOWA" provider="youtube" %}
+
+To embed it as a video header you'd use the following YAML Front Matter
+
+```yaml
+header:
+  video:
+    id: XsxDH4HcOWA
+    provider: youtube
+```
+
+### Vimeo
+
+To embed the following Vimeo video at url `https://vimeo.com/97649261` into a post or page's main content you'd use: 
+
+```liquid
+{% raw %}{% include video id="97649261" provider="vimeo" %}{% endraw %}
+```
+
+{% include video id="97649261" provider="vimeo" %}
+
+To embed it as a video header you'd use the following YAML Front Matter
+
+```yaml
+header:
+  video:
+    id: 97649261
+    provider: vimeo
+```