Add meta description tag to Lux homepage

[nikdragovic]

We need to add a meta description to Lux in order to provide a helpful snippet of explanatory text for users who find it via search engine. It will also help with SEO in these search engines.

Acceptance Criteria

• [ ] The following text should be applied to the homepage HTML (one possible version shown; edits to structure are at developer discretion).

<meta content="The digital front door to the unique cultural heritage and scholarship material from Emory Libraries. Discover, view, and download images, books, and more from our campus repositories." name="description"/>

[bwatson78]

PR made: https://github.com/emory-libraries/dlp-lux/pull/622

[nikdragovic]

@bwatson78 Tested, thanks!