maintainers: add GirardR1006

maintainers/maintainer-list.nix

···
     githubId = 471835;
     name = "Giorgio Gallo";
   };
+  GirardR1006 = {
+    email = "[e-mail]";
+    github = "GirardR1006";
+    githubId = 19275558;
+    name = "Julien Girard-Satabin";
+  };
   GKasparov = {
     email = "[e-mail]";
     github = "GKasparov";