maintainers: add sxmair

Signed-off-by: Syed Sumairul Hasan <[e-mail]>

maintainers/maintainer-list.nix

···
     githubId = 332289;
     name = "Rafał Łasocha";
   };
+  sxmair = {
+    email = "[e-mail]";
+    github = "sxmair";
+    githubId = 127287939;
+    name = "Syed Sumairul Hasan";
+  };
   syberant = {
     email = "[e-mail]";
     github = "syberant";