Clean up and annotate CODEOWNERS (#23678)

Summary:
Trivial PR. Cleaning up the CODEOWNERS file a bit.

[GENERAL] [Changed] - Clean up and annotate CODEOWNERS on GitHub
Pull Request resolved: https://github.com/facebook/react-native/pull/23678

Differential Revision: D14253726

Pulled By: cpojer

fbshipit-source-id: ffb47c18b7078b7489dadb352cdaa5ffea0d0aea

.github/CODEOWNERS

@@ -1,11 +1,37 @@
-Libraries/Animated/* @janicduplessis
-Libraries/NativeAnimation/* @janicduplessis
-Libraries/Image/* @shergin
-Libraries/Text/* @shergin
+# See https://help.github.com/en/articles/about-code-owners
+# to learn more about code owners.
+# Order is important; the last matching pattern takes the most
+# precedence. You may specify either a GitHub username, or an
+# email address if you prefer, as the code owner.
+
+# Any Markdown file anywhere in the repository
+**/*.md @hramos @cpojer
+
+# GitHub Settings, Bots
+/.github/ @hramos
+/bots @hramos
+
+# Continuous Integration
+/.circleci/ @hramos
+/.circleci/Dockerfiles @gengjiawen
+/.appveyor/ @gengjiawen
+
+# Internals
 React/Base/* @shergin
 React/Views/* @shergin
 React/Modules/* @shergin
 React/CxxBridge/* @mhorowitz
+
+# Components and APIs
 ReactAndroid/src/main/java/com/facebook/react/animated/* @janicduplessis
-**/*.md @hramos @cpojer
-package.json @hramos @cpojer
+Libraries/Animated/* @janicduplessis
+Libraries/NativeAnimation/* @janicduplessis
+Libraries/Image/* @shergin
+Libraries/Text/* @shergin
+
+# Modifications to package.json typically require 
+# additional effort from a Facebook employee to land
+/package.json @hramos @cpojer
+
+# These should not be modified through a GitHub PR
+LICENSE* @hramos @cpojer @yungsters