Add TypeScript typings file

index.d.ts

@@ -0,0 +1 @@
+export function exec(cmd: string, options: { name?: string, icns?: string }, callback: (error: string, stdout: string, stderr: string) => void): void;

package.json

@@ -3,6 +3,7 @@
   "version": "9.0.0",
   "description": "Run a command using sudo, prompting the user with an OS dialog if necessary",
   "main": "index.js",
+  "types": "index.d.ts",
   "files": [
     "LICENSE",
     "README.md",