Add CODEOWNERS file (open-telemetry#2)

* Add CODEOWNERS file

* Update CODEOWNERS

Author: bogdandrutu

.github/CODEOWNERS

@@ -0,0 +1,15 @@
+#####################################################
+#
+# List of approvers for OpenTelemetry Collector Builder
+#
+#####################################################
+#
+# Learn about membership in OpenTelemetry community:
+#  https://github.com/open-telemetry/community/blob/master/community-membership.md
+#
+#
+# Learn about CODEOWNERS file format:
+#  https://help.github.com/en/articles/about-code-owners
+#
+
+* @open-telemetry/collector-approvers @open-telemetry/collector-builder-approvers