Create CODEOWNERS

CODEOWNERS

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+# This file is a list of the people responsible for ensuring that patches for a
+# particular part of Swift are reviewed, either by themselves or by someone else.
+# They are also the gatekeepers for their part of Swift, with the final word on
+# what goes in or not.
+#
+# The list is sorted by surname and formatted to allow easy grepping and
+# beautification by scripts.  The fields are: name (N), email (E), web-address
+# (W), PGP key ID and fingerprint (P), description (D), and snail-mail address
+# (S).
+
+* @shahmishal @cmcgee1024