add softonic to adopters

Signed-off-by: Riccardo Piccoli <riccardo.piccoli@softonic.com>

ADOPTERS.md

@@ -10,6 +10,7 @@
 - [Microsoft](https://microsoft.com)
 - [Qovery](https://www.qovery.com/)
 - [Samsung SDS](https://www.samsungsds.com/)
+- [Softonic](https://hello.softonic.com/)
 - [Ville de Montreal](https://montreal.ca)
 
 _This file is part of the CNCF official documentation for projects._