Add XWiki to "Who is using Testcontainers" (#2117)

Author: vmassol

docs/index.md

@@ -78,6 +78,7 @@ You can also [check the latest version available on Maven Central](https://searc
 * [wescale](https://www.wescale.com) - Integration testing against HTTP service mocks and various data stores
 * [Marquez](https://marquezproject.github.io/marquez) - PostgreSQL integration testing
 * [Transferwise](https://transferwise.com/) - Integration testing for different RDBMS, kafka and micro services
+* [XWiki](https://xwiki.org) - [Testing XWiki](https://dev.xwiki.org/xwiki/bin/view/Community/Testing/DockerTesting/) under all [supported configurations](https://dev.xwiki.org/xwiki/bin/view/Community/SupportStrategy/)
 
 ## License