feat(showcase): add Patreon Blog and Full Beaker sites (#9916)

<!--
  Q. Which branch should I use for my pull request?
  A. Use `master` branch (probably).

  Q. Which branch if my change is a bug fix for Gatsby v1?
  A. In this case, you should use the `v1` branch

  Q. Which branch if I'm still not sure?
  A. Use `master` branch. Ask in the PR if you're not sure and a Gatsby maintainer will be happy to help :)

  Note: We will only accept bug fixes for Gatsby v1. New features should be added to Gatsby v2.

  Learn more about contributing: https://www.gatsbyjs.org/docs/how-to-contribute/
-->

docs/sites.yml

@@ -3317,3 +3317,19 @@
     - Technology
     - Nonprofit
   featured: false
+- title: Patreon Blog
+  url: https://blog.patreon.com/
+  main_url: https://blog.patreon.com/
+  description: >-
+    Official blog of Patreon.com
+  categories:
+    - Blog
+  featured: false
+- title: Full Beaker
+  url: https://fullbeaker.com/
+  main_url: https://fullbeaker.com/
+  description: >-
+    Full Beaker provides independent advice online about careers and home ownership, and connect anyone who asks with companies that can help them.
+  categories:
+    - Consulting
+  featured: false