github: add codeowners file

Initial version.

See https://help.github.com/articles/about-codeowners/

.github/CODEOWNERS

@@ -0,0 +1,21 @@
+# https://help.github.com/articles/about-codeowners/
+#
+# last match wins, so put more specific matches towards the end
+
+*                   @OISF/core-team
+rust/*              @victorjulien @jasonish
+src/source-*        @regit
+doc/*               @norg
+src/detect-engine*  @victorjulien
+*ssl*               @thus @OISF/core-team
+*tls*               @thus @OISF/core-team
+*nfs*               @victorjulien
+*dns*               @jasonish
+*ntp*               @chifflier
+
+*prelude*           @ToToL
+
+*napatech*          @psanders240
+
+.github/            @victorjulien
+