docs(autofocus): not documented well

[arlowhite]

I wanted the functionality of md-autofocus, but never came across a reference to it in the documentation. (It is only mentioned in md-autocomplete) The only way I found out about it was through github issue comments.

Please document md-autofocus in a few more places so developers are more aware of it.

• Add md-autofocus to the list of attributes in mdInput
• Mention md-autofocus in mdDialog.

Lower priority (additional ideas)

• Add reference to it from other containers similar to mdDialog
• Mention md-autofocus in all input directives that support it: md-contact-chips, md-checkbox, etc. However, this is much more work, and I think if it's in md-input, developers will assume they can use it on these other input components.
• Add an Attribute Directives section in the documentation to document md-autofocus in more detail.

[amritk]

+1