Add CODEOWNERS file

Author: trask

.github/CODEOWNERS

@@ -0,0 +1,10 @@
+#
+# Learn about membership in OpenTelemetry community:
+#  https://github.com/open-telemetry/community/blob/main/guides/contributor/membership.md
+#
+#
+# Learn about CODEOWNERS file format:
+#  https://help.github.com/en/articles/about-code-owners
+#
+
+* @adrielp @austinlparker @trask