Document how to pass HTML value using variable instead of tag attribute

[eliot-akira]

From:

• L&L Template with Local Variable acf_oembed or wysiwyg is not being rendered framework#6

To be documented:

• Limitation of passing HTML in a tag attribute using the {} syntax, which only supports simple values.
• Workaround using variable

Example:

Use a variable to pass HTML content to a template.

<Set modal_content>
  <Field acf_oembed=best_industry_focus_video />
</Set>

<Template name=modal />

And to get the value in the template:

<Get modal_content />

This way, the HTML content doesn't need to go through a tag attribute.