add code owners file (#141)

* add code owners file

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* add requested user

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

.github/CODEOWNERS

@@ -0,0 +1,3 @@
+# automatically requests pull request reviews for files matching the given pattern; the last match takes precedence
+
+*       @spacetelescope/roman_datamodels-maintainers @WilliamJamieson