[DOCS] Updates Changelog for 9.x

Author: picandocodigo

CHANGELOG-9.x.md

@@ -1,14 +1,19 @@
 # CHANGELOG 9.x
 
+## Gem
+
+The size of both `elasticsearch` and `elasticsearch-api` gems will be smaller, since some unnecessary files that were being included in the gem have been removed.
+
+The required Ruby version is set to `2.6` to keep compatiblity wit JRuby 9.3. However, we only test the code against currently supported Ruby versions.
+
 ## Elasticsearch API
 
 ### Development
 
-**Integration Tests**
-
-Migrated away from the Elasticsearch REST API tests and test runner in CI. We now run the [Elasticsearch Client tests](https://github.com/elastic/elasticsearch-clients-tests/) with the [Elasticsearch Tests Runner](https://github.com/elastic/es-test-runner-ruby/**. This gives us more control on what we're testing and makes the Buildkite build way faster in Pull Requests and scheduled builds.
+#### Testing
 
+Migrated away from the Elasticsearch REST API tests and test runner in CI. We now run the [Elasticsearch Client tests](https://github.com/elastic/elasticsearch-clients-tests/) with the [Elasticsearch Tests Runner](https://github.com/elastic/es-test-runner-ruby). This gives us more control on what we're testing and makes the Buildkite build way faster in Pull Requests and scheduled builds.
 
-**Rake tasks**
+#### Rake tasks
 
 Some old rake tasks that were not being used have been removed. The rest were streamlined, the `es` namespace has been streamlined to make it easier to run Elasticsearch with Docker during development. The `docker` namespace was merged into `es`.