[DOCS] Update API ref link in docs README (#124069)

https://github.com/elastic/elasticsearch-specification/pull/3873/files

Author: leemthompo

docs/README.md

@@ -17,7 +17,7 @@ Docs live in **three places**:
 
 1. **Reference content** lives in this repo. This covers low-level stuff like settings and configuration information that is tightly coupled to code.
 - 👩🏽‍💻 **Engineers** own the bulk of this content.
-2.  **API reference docs** live in the [Elasticsearch specification](https://github.com/elastic/elasticsearch-specification)
+2.  **API reference docs** live in the [Elasticsearch specification](https://github.com/elastic/elasticsearch-specification/blob/main/README.md#how-to-generate-the-openapi-representation)
     - This is where you need to update API docs published in the [new API docs system](https://www.elastic.co/docs/api/doc/elasticsearch/v8/)
 - 👩🏽‍💻 **Engineers** own this content.
 3. **Narrative, overview, and conceptual content** mostly lives in the [`docs-content`](https://github.com/elastic/docs-content/) repo. 
@@ -106,4 +106,4 @@ This allows slightly more expressive testing of the snippets. Since that syntax
 % TEST[s/\n$/\nstartyaml\n  - compare_analyzers: {index: thai_example, first: thai, second: rebuilt_thai}\nendyaml\n/]
 ```
 
-Any place you can use json you can use elements like `$body.path.to.thing` which is replaced on the fly with the contents of the thing at `path.to.thing` in the last response.
+Any place you can use json you can use elements like `$body.path.to.thing` which is replaced on the fly with the contents of the thing at `path.to.thing` in the last response.