doc: fix badge

README.md

@@ -4,7 +4,8 @@ This repository contains the complete documentation related to
 [**Rotare**][rotare-repo], a feature-rich and open-source implementation of the
 Blade Element Momentum Theory in MATLAB.
 
-![https://img.shields.io/badge/Documentation-PDF-yellow?style=for-the-badge](https://rotare.gitlabpages.uliege.be/documentation/rotare-doc.pdf)
+[![Documentation
+PDF](https://img.shields.io/badge/Documentation-PDF-yellow?style=for-the-badge)](https://rotare.gitlabpages.uliege.be/documentation/rotare-doc.pdf)
 
 ## IMPORTANT NOTE
 **Rotare is still currently in development. As long as it is not in v1.0.0, the