Adding custom text inside an automatically generated output from an array

I have the following code:

$feed->item([
    'title' => $post->title,
    'guid' => $post->guid
]); 

which generates the following output for me:

<title>Title of post</title>
<guid>Guid of the post</guid>

I want to include the following tag in it

<enclosure url="image.jpg" length="1" type="image/jpeg"/>

How this will be possible, considering that the code above, generated automatically an opening and closure tag for each attribute.

PS: The library im using is: https://github.com/thujohn/rss-l4

via Chebli Mohamed