Add custom nixvim in overlay

flake.nix

@@ -85,6 +85,7 @@
         gh-rebase-pr = final.callPackage ./derivations/gh-rebase-pr {};
         wlman = final.callPackage ./derivations/wlman {};
         check-certificate-revocation = final.callPackage ./derivations/check-certificate-revocation {};
+        neovim = self.packages.${system}.nixvim;
         # https://kokada.capivaras.dev/blog/quick-bits-realise-nix-symlinks/
         realise-symlink = final.writeShellApplication {
             name = "realise-symlink";