HSEARCH-4170 Mention in the documentation that Elasticsearch 7.11 is …

…not open-source

Signed-off-by: Yoann Rodière <yoann@hibernate.org>

CONTRIBUTING.md

@@ -204,7 +204,7 @@ The following profiles are available:
  * `elasticsearch-7.7` for 7.7
  * `elasticsearch-7.8` for 7.8 to 7.9
  * `elasticsearch-7.10` for 7.10 (the default)
- * `elasticsearch-7.11` for 7.11+
+ * `elasticsearch-7.11` for 7.11+ ([not open-source](https://opensource.org/node/1099))
 
 A list of available versions for `test.elasticsearch.connection.version` can be found on
 [Maven Central](https://search.maven.org/search?q=g:org.elasticsearch%20AND%20a:elasticsearch&core=gav).

documentation/src/main/asciidoc/reference/getting-started.asciidoc

@@ -33,6 +33,16 @@ https://hibernate.org/search/releases/#compatibility-matrix[compatibility matrix
 The https://hibernate.org/community/compatibility-policy/[compatibility policy] may also be of interest.
 ====
 
+[NOTE]
+.Elasticsearch 7.11+ licensing
+====
+While Elasticsearch up to 7.10 was distributed under the Apache License 2.0,
+be aware that Elasticsearch 7.11 and later are distributed under the Elastic License and the SSPL,
+which are https://opensource.org/node/1099[not considered open-source by the Open Source Initiative].
+
+Only the low-level Java REST client, which Hibernate Search depends on, remains open-source.
+====
+
 [[getting-started-migrating]]
 == Migration notes