docs: storage: show better getSignedUrl examples

lib/storage/file.js

@@ -1156,11 +1156,53 @@ File.prototype.getSignedPolicy = function(options, callback) {
  * @param {string} callback.url - The signed URL.
  *
  * @example
+ * var TWO_WEEKS_MS = Math.round(Date.now() / 1000) + (60 * 60 * 24 * 14);
+ *
+ * //-
+ * // Generate a URL that allows temporary access to download your file.
+ * //-
+ * var request = require('request');
+ *
  * file.getSignedUrl({
  *   action: 'read',
- *   expires: Math.round(Date.now() / 1000) + (60 * 60 * 24 * 14), // 2 weeks.
- *   promptSaveAs: 'filename.ext'
- * }, function(err, url) {});
+ *   expires: TWO_WEEKS_MS
+ * }, function(err, url) {
+ *   if (err) {
+ *     console.error(err);
+ *     return;
+ *   }
+ *
+ *   // The file is now available to read from this URL.
+ *   request(url, function(err, resp) {
+ *     // resp.statusCode = 200
+ *   });
+ * });
+ *
+ * //-
+ * // Generate a URL to allow write permissions. This means anyone with this URL
+ * // can send a POST request with new data that will overwrite the file.
+ * //-
+ * file.getSignedUrl({
+ *   action: 'write',
+ *   expires: TWO_WEEKS_MS
+ * }, function(err, url) {
+ *   if (err) {
+ *     console.error(err);
+ *     return;
+ *   }
+ *
+ *   // The file is now available to be written to.
+ *   var writeStream = request.post(url);
+ *   writeStream.end('New data');
+ *
+ *   writeStream.on('complete', function(resp) {
+ *     // Confirm the new content was saved.
+ *     file.download(function(err, fileContents) {
+ *       console.log('Contents:', fileContents.toString());
+ *       // Contents: New data
+ *     });
+ *   });
+ * });
  */
 File.prototype.getSignedUrl = function(options, callback) {
   if (options.expires < Math.floor(Date.now() / 1000)) {