Add Hotdata to the "known users" list in introduction.md (apache#23004)

## Rationale for this change

Add hotdata to known users list

Co-authored-by: Andrew Lamb <andrew@nerdnetworks.org>

Author: zfarrell

docs/source/user-guide/introduction.md

@@ -112,6 +112,7 @@ Here are some active projects using DataFusion:
 - [GreptimeDB] Open Source & Cloud Native Distributed Time Series Database
 - [hiop](https://hiop.io) Serverless Data Logistic Platform
 - [HoraeDB] Distributed Time-Series Database
+- [Hotdata](https://www.hotdata.dev) On-demand databases for AI agents with a unified query engine for vector, OLAP, and full-text search.
 - [Iceberg-rust](https://github.com/apache/iceberg-rust) Rust implementation of Apache Iceberg
 - [InfluxDB] Time Series Database
 - [Kamu] Planet-scale streaming data pipeline