Add description for the tempFilePath.

Add description for the tempFilePath file parameter.

README.md

@@ -41,6 +41,7 @@ The **req.files.foo** object will contain the following:
 * `req.files.foo.mv`: A function to move the file elsewhere on your server
 * `req.files.foo.mimetype`: The mimetype of your file
 * `req.files.foo.data`: A buffer representation of your file
+* `req.files.foo.tempFilePath`: A path to the temporary file in case useTempFiles option was set to true.
 * `req.files.foo.truncated`: A boolean that represents if the file is over the size limit
 * `req.files.foo.size`: Uploaded size in bytes
 * `req.files.foo.md5`: MD5 checksum of the uploaded file