docs(container): add registry_sha256 (#2320)

Author: Codelax

docs/resources/container.md

@@ -78,6 +78,8 @@ The following arguments are optional:
 
 - `registry_image` - (Optional) The registry image address. e.g: **"rg.fr-par.scw.cloud/$NAMESPACE/$IMAGE"**.
 
+- `registry_sha256` - (Optional) The sha256 of your source registry image, changing it will re-apply the deployment. Can be any string.
+
 - `max_concurrency` - (Optional) The maximum number of simultaneous requests your container can handle at the same time. Defaults to 50.
 
 - `protocol` - (Optional) The communication [protocol](https://developers.scaleway.com/en/products/containers/api/#protocol-9dd4c8) http1 or h2c. Defaults to http1.