doc: add README files for components (#6653)

* docs: add README for components

* Update README.md

Co-authored-by: Antoine Bluchet <soyuka@users.noreply.github.com>

* Update README.md

Co-authored-by: Antoine Bluchet <soyuka@users.noreply.github.com>

* Update README.md

Co-authored-by: Antoine Bluchet <soyuka@users.noreply.github.com>

* remove trailing spaces

* typo

* better title

---------

Co-authored-by: Antoine Bluchet <soyuka@users.noreply.github.com>

Author: dunglas

README.md

@@ -1,3 +1,12 @@
 # API Platform - GraphQL
 
-Build GraphQL API endpoints
+The [GraphQL](https://graphql.org/) component of the [API Platform](https://api-platform.com) framework.
+
+[Documentation](https://api-platform.com/docs/core/graphql/)
+
+> [!CAUTION]
+>
+> This is a read-only sub split of `api-platform/core`, please
+> [report issues](https://github.com/api-platform/core/issues) and
+> [send Pull Requests](https://github.com/api-platform/core/pulls)
+> in the [core API Platform repository](https://github.com/api-platform/core).