Update sites.yml (#11148)
Update sites.yml (#11148)

Added two recent Gatsby sites to the Showcase: an opera singer and a health-related charity.
gatsbyjs/gatsby,ChristopherBiscardi/gatsby,gatsbyjs/gatsby,ChristopherBiscardi/gatsby,gatsbyjs/gatsby,gatsbyjs/gatsby,ChristopherBiscardi/gatsby,gatsbyjs/gatsby,ChristopherBiscardi/gatsby,gatsbyjs/gatsby