Have website hint search engines to use the icons and screenshots

https://github.com/jekyll/jekyll-seo-tag/blob/master/docs/usage.md

The SEO tag will respect the following YAML front matter if included in a post, page, or document:

- `title` - The title of the post, page, or document
- `description` - A short description of the page's content
- `image` - URL to an image associated with the post, page, or document (e.g., /assets/page-pic.jpg)
- `author` - Page-, post-, or document-specific author information (see Advanced usage)
- `lang` - Page-, post-, or document-specific language information

We should make sure that we are using those tags, especially the first three. This will hopefully get the applications displayed nicely in search engines.