Update MAINTAINERS to include environment files
To be maintained by me (Joe) and reviewed by Wolfgang Denk when
available.
Signed-off-by: 
Joe Hershberger <joe.hershberger@ni.com>
To be maintained by me (Joe) and reviewed by Wolfgang Denk when
available.
Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>