docs: Resolves broken header image link
<h1 align="center" style="margin-bottom: 8px">
- <img alt="Hydra - cloud native access control" src="../images/logo-essential.png">
+ <img alt="Hydra - cloud native access control" src="./images/logo-essential.png">
</h1>
<h4 style="margin: 0 20% 1.275em" align="center">
