maintainers: add stnley

maintainers/maintainer-list.nix

···
     githubId = 1694705;
     name = "Sam Stites";
   };
+  stnley = {
+    email = "[e-mail]";
+    github = "stnley";
+    githubId = 64174376;
+    name = "Michael Stanley";
+  };
   strager = {
     email = "[e-mail]";
     github = "strager";