doc: mention quicker way to build docs

`make doc-only` skips the process of building Node, which speeds
things up considerably for new contributors.

doc/contributing/api-documentation.md

@@ -4,9 +4,8 @@ The Node.js API documentation is generated by an in-house tooling that resides
 within the [tools/doc](https://github.com/nodejs/node/tree/main/tools/doc)
 directory.
 
-The build process (using `make doc`) uses this tooling to parse the markdown
-files in [doc/api](https://github.com/nodejs/node/tree/main/doc/api) and
-generate the following:
+The build process (using `make doc` or `make doc-only`) uses this tooling to
+parse the markdown files in [`doc/api`][] and generate the following:
 
 1. Human-readable HTML in `out/doc/api/*.html`
 2. A JSON representation in `out/doc/api/*.json`
@@ -302,3 +301,5 @@ mutate the data and appends it to the final JSON object.
 
 For a more in-depth information we recommend to refer to the `json.mjs` file as
 it contains a lot of comments.
+
+[`doc/api`]: https://github.com/nodejs/node/tree/main/doc/api