chore(github): add CODEOWNERS (#10)

.github/CODEOWNERS

@@ -0,0 +1,10 @@
+# Order is important. The last matching pattern takes precedence. See:
+# https://docs.github.com/en/repositories/managing-your-repositorys-settings-and-features/customizing-your-repository/about-code-owners
+
+# DEFAULT OWNERS
+* @mdn/core-dev
+
+# These are @mdn-bot because the auto-merge GHA workflow uses the PAT of this account.
+# If another reviewer is specified, update the PAT token or auto-merge will cease to be automatic.
+/package.json @mdn-bot
+/package-lock.json @mdn-bot