chore(install): symlink nwjs to nwjs-VERSION-PLATFORM-ARCH dir

This allows `nw-builder` to access the downloaded binaries by setting
`cacheDir` to `./node_modules/nw`

Fixes: #128

lib/install.js

@@ -1,5 +1,5 @@
 const { createWriteStream, existsSync } = require('node:fs');
-const { rename, rm } = require('node:fs/promises');
+const { rename, rm, symlink } = require('node:fs/promises');
 const { get } = require('node:https');
 const { resolve } = require('node:path');
 const { arch, env, platform, exit } = require('node:process');
@@ -219,5 +219,8 @@ async function install() {
     nwDir
   );
 
+  // This allows nw-builder to treat ./node_modules/nw as cacheDir and access the downloaded binary.
+  await symlink(nwDir, nwFile);
+
   return;
 }