Update CONTRIBUTING.md
Add myself to contributors
@@ -61,3 +61,4 @@ To accept, please:
| Sanket Sawant | | Mumbai, India | 2017-12-09 |
| Pablo Tirado | | Madrid, Spain | 2018-01-05 |
| Gokhan Kuyucak | | Izmir, Turkey | 2018-01-14 |
+| Guido Grazioli | | London, United Kingdom | 2018-01-15 |
