add bdimcheff as maintainer

lib/maintainers.nix

···
   aycanirican = "Aycan iRiCAN <[e-mail]>";
   balajisivaraman = "Balaji Sivaraman<[e-mail]>";
   bbenoist = "Baptist BENOIST <[e-mail]>";
+  bdimcheff = "Brandon Dimcheff <[e-mail]>";
   bennofs = "Benno Fünfstück <[e-mail]>";
   berdario = "Dario Bertini <[e-mail]>";
   bergey = "Daniel Bergey <[e-mail]>";