Add default CODEOWNERS (#302)

Update CODEOWNERS

Add content-team and learn to codeowners

Author: pransh15

.github/CODEOWNERS

@@ -5,6 +5,8 @@
 # See: https://docs.github.com/en/repositories/managing-your-repositorys-settings-and-features/customizing-your-repository/about-code-owners
 # ----------------------------------------------------------------------------
 
+* @mdn/content-team @mdn/learn
+
 /.github/workflows/ @mdn/engineering
 /.github/CODEOWNERS @mdn/engineering
 /SECURITY.md @mdn/engineering