Standardize one click templates

[KaneFreeman]

All one click templates regardless of site site generator, should have the following:

• ~Same starting content / admin config.yml setup~ May revisit later
• ~Same previews / styles~ May revisit later
• Standardized readmes
• Add renovate

Templates:

• [x] Hugo Site Starter
• [x] Gatsby Site Starter
• [ ] Middleman Site Starter
• [ ] Preact
• [x] Next.js Blog Template
• [ ] Eleventy Starter
• [ ] Nuxt.js Boilerplate
• [ ] Metalsmith Starter

Related to #25

[KaneFreeman]

Will revisit in the future. Probably when templates are moved into this monorepo.