Add in data contract playground to vendors

vendors.md

@@ -10,6 +10,7 @@ catalogs, data quality platforms, security tools, and more.
 * [Data Caterer](https://data.catering/setup/guide/data-source/metadata/open-data-contract-standard/) - Test data
   management tool using data contracts as a metadata source
 * [Data Contract CLI](https://cli.datacontract.com) - Open Source tooling around data contracts
+* [Data Contract Playground](https://data-catering.github.io/data-contract-playground/) - Playground site for creating, exporting and validating data contracts
 * [DQC.ai | DQ PLATFORM](https://www.dqc.ai/dqc-platform) - [Enhancing Data Quality with ODCS: A Standard Ensured by the DQ Platform
   ](https://www.dqc.ai/post/enhancing-data-quality-with-odcs-a-standard-ensured-by-the-dq-platform)