enable minimal syntax highlighting

package.json

@@ -21,7 +21,8 @@
       "first-line-regex": "^#!.*\\bnix-shell\\b.*$",
       "content-regex": "^\b$nix-shell wraps other languages so intentionally fail against (and yield to) those other language matches",
       "injection-regex": "^(nix[-_]?shell)$",
-      "scope": "source.nix_shell"
+      "scope": "source.nix_shell",
+      "highlights": [ "queries/highlights.scm" ]
     }
   ]
 }

queries/highlights.scm

@@ -0,0 +1 @@
+(nix_shell_directive) @keyword