Add Leonardo Giordani to AUTHORS for his contributions

AUTHORS.md

@@ -11,6 +11,7 @@ And Pelican Bootstrap 3 would not have been possible without the outstanding con
 - [Sagar Behere](https://github.com/sagarbehere) aka `sagarbehere`
 - [Romulo Jales](https://github.com/romulojales) aka `romulojales`
 - [Mike Abrahamsen](https://github.com/mikeabrahamsen) aka `mikeabrahamsen`
+- [Leonardo Giordani](https://github.com/lgiordani) aka `lgiordani`
 
 (For a full contribution overview [look here](https://github.com/DandyDev/pelican-bootstrap3/graphs/contributors).
 If you name is missing, please tell me!)
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