update docs

Author: vincentsarago

README.md

@@ -43,7 +43,12 @@ For more than millions of records it is recommended to either set a low connecti
 
 ### Hydration
 
-To configure **stac-fastapi-pgstac** to [hydrate search result items in the API](https://stac-utils.github.io/pgstac/pgstac/#runtime-configurations), set the `USE_API_HYDRATE` environment variable to `true` or explicitly set the option in the PGStac Settings object.
+To configure **stac-fastapi-pgstac** to [hydrate search result items at the API level](https://stac-utils.github.io/pgstac/pgstac/#runtime-configurations), set the `USE_API_HYDRATE` environment variable to `true`. If `false` (default) the hydration will be done in the database.
+
+| use_api_hydrat (API) | nohydrate (PgSTAC) | Hydration |
+|                  --- |                --- |       --- |
+|                False |              False |    PgSTAC |
+|                 True |               True |       API |
 
 ### Migrations