Create CODEOWNERS (optimizely#340)

CODEOWNERS

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+# This is a comment.
+# Each line is a file pattern followed by one or more owners.
+
+  # These owners will be the default owners for everything in the repo.
+# Unless a later match takes precedence, @global-owner1 and @global-owner2
+# will be requested for review when someone opens a pull request.
+*       @optimizely/fullstack-devs
+
+  # Order is important; the last matching pattern takes the most precedence.
+# When someone opens a pull request that only modifies JS files, only @js-owner
+# and not the global owner(s) will be requested for a review.
+#*.js    @js-owner
+
+  # You can also use email addresses if you prefer. They'll be used to look up
+# users just like we do for commit author emails.
+#docs/*  [email protected]