Update introduction.md

I tried with vultr object storage and it is working

Author: jeremielondon

docs/knowledge-base/s3/introduction.md

@@ -14,6 +14,7 @@ Currently supported S3 compatible storages are:
 - Scaleway Object Storage
 - Hetzner S3 Storage (beta)
 - Wasabi hot cloud storage
+- Vultr
 
 Other's could work, but not tested yet. If you test it, please let us know.