feat: nixvim config

currently only for dnsc-air. can simply be imported in other hosts

modules/nixvim/completion.nix

@@ -0,0 +1,21 @@
+{
+  plugins.blink-cmp = {
+    enable = true;
+    settings = {
+      keymap = {
+        preset = "default";
+      };
+      appearance = {
+        nerd_font_variant = "mono";
+      };
+      completion = {
+        documentation = {
+          auto_show = false;
+        };
+      };
+      signature = {
+        enabled = true;
+      };
+    };
+  };
+}