Add Derek control file

I want to start using Derek to check for Signed-off-by (or, more explicitly,
the DCO) in pull requests.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

.DEREK.yml

@@ -0,0 +1,13 @@
+maintainers:
+ - dirkhh
+ - neolit123
+ - atdotde
+ - torvalds
+ - glance-
+ - mturkia
+ - janmulder
+ - tcanabrava
+
+features:
+ - dco_check
+ - comments