How to add text in a box with a leader to a plot?
<p>I know how to write text in a plot, but this is a bit more complicated. Below is a rough illustration of how I want my text to be (I did it in plain paint).</p>

<p>Fig:</p>

<p><a href="https://i.stack.imgur.com/AvdP5.png" rel="nofollow"><img src="https://i.stack.imgur.com/AvdP5.png" alt="The desired result"></a></p>

<p>I want to have a little long arrow and a box around the text. </p>