Add a new CODEOWNERS file, and add a few owners.

Signed-off-by: Daniel Nephin <dnephin@docker.com>

.github/CODEOWNERS

@@ -0,0 +1,8 @@
+# Github code owners
+# See https://github.com/blog/2392-introducing-code-owners
+
+cli/compose/*              @dnephin @vdemeester
+contrib/completion/bash/*  @albers
+contrib/completion/zsh/*   @sdurrheimer
+docs/*                     @mstanleyjones @vdemeester @thaJeztah
+scripts/*                  @dnephin