Add semantic layers to readme

Author: stevebissett

README.md

@@ -89,6 +89,9 @@ Top must-join communities for ML:
   - [dlt](https://dlthub.com/)
   - [Sling](https://slingdata.io/)
   - [Meltano](https://meltano.com/)
+ - Semantic Layers
+  - [Cube](https://cube.dev)
+  - [dbt Semantic Layer](https://www.getdbt.com/product/semantic-layer) 
 - Modern OLAP
   - [Apache Druid](https://druid.apache.org/)
   - [ClickHouse](https://clickhouse.com/)