Add CODEOWNERS file

Code owners are automatically requested for review when someone opens a
pull request that modifies code that they own. For more info:
https://docs.github.com/en/repositories/managing-your-repositorys-settings-and-features/customizing-your-repository/about-code-owners#about-code-owners

Author: mhucka

.github/CODEOWNERS

@@ -0,0 +1,5 @@
+# Summary: define who is automatically requested for review when someone opens
+# a pull request that affects specified paths.
+
+# Set Tesseract Team for everything.
+* @quantum-lib/tesseract-team