maintainers: add mtpham99

maintainers/maintainer-list.nix

···
     githubId = 2176611;
     name = "Marko Poikonen";
   };
+  mtpham99 = {
+    name = "Matthew Pham";
+    email = "[e-mail]";
+    github = "mtpham99";
+    githubId = 72663763;
+    keys = [ { fingerprint = "DB3E A12D B291 594A 79C5 F6B3 10AB 6868 37F6 FA3F"; } ];
+  };
   mtreca = {
     email = "[e-mail]";
     github = "mtreca";