[DOCS] Updates README

Author: picandocodigo

README.md

@@ -6,12 +6,32 @@ This repository holds common tests for Elasticsearch Clients.
 
 The tests are specified using the Elasticsearch YAML format reported [here](https://github.com/elastic/elasticsearch/blob/main/rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/README.asciidoc).
 
-All the tests for serverless are located in the [tests](tests) folder. Each API endpoint has a folder
-containing the tests to be executed. All the files must be executed in order, they are enumerated with
-a digit prefix.
+All the tests are located in the [tests](tests) folder. Each API endpoint has a folder containing the tests to be executed. All the files must be executed in order, they are enumerated with a digit prefix.
+
+## Test Sections
+
+### `requires`
+
+This section should define if a test is available for the stack client, serverless client or both with the following format:
+```yaml
+---
+requires:
+  serverless: true
+  stack: true
+```
+
+This helps us differentiate tests for a particular client and define tests in common for both.
 
 ### `setup` and `teardown`
 
 Pre-requisites to run a test (e.g. creating an index, populating an index with data) are declared in a `setup` section. The list of commands in the `setup` section has to run before the test section.
 
 Cleanup is declared in a `teardown` section. This list of commands will run after the tests. **Please add a `teardown` section to your test to remove any created artifacts and data**. This will keep our test clusters clean and our test suite sane.
+
+## APIs Report
+
+[This report](https://github.com/elastic/elasticsearch-clients-tests/blob/main/apis_report.md) contains information from each specification:
+- [Elasticsearch REST API JSON specification](https://github.com/elastic/elasticsearch/tree/main/rest-api-spec)
+- [Elasticsearch API Specification](https://github.com/elastic/elasticsearch-specification/)
+
+It also contains information on test coverage in this project for Serverless and Stack APIs. The report is automatically generated when code is pushed in a [GitHub Action](https://github.com/elastic/elasticsearch-clients-tests/blob/main/.github/workflows/report.yml). It can also be triggered manually. The source code for the report is in the [./report/](./report) directory.