Add CODEOWNERS file

References:
* https://github.com/usnistgov/opensource-repo/#codeowners

Signed-off-by: Alex Nelson <[email protected]>

Author: ajnelson-nist

.github/CODEOWNERS

@@ -0,0 +1,10 @@
+# This file lists the contributors responsible for the
+# repository content. They will also be automatically
+# asked to review any pull request made in this repository.
+
+# Each line is a file pattern followed by one or more owners.
+# The sequence matters: later patterns take precedence.
+
+# FILES  OWNERS
+*        @casework/maintainers-global
+*        @casework/maintainers-case-python-utilities