docs: add note about json-ld filepath (backport #1983) (#1984)

Co-authored-by: Ryan Christoffersen <12519942+ryanchristo@users.noreply.github.com>

docs/tutorials/user/credit-class-project-batch-management.md

@@ -240,6 +240,8 @@ Once we have the supporting data for a credit class, project, and batch, we can
 curl -X GET -d '<json-ld>' -H "Content-Type: application/json" https://api.registry.regen.network/iri-gen
 ```
 
+In the above example, you can also use a filepath instead of the raw JSON-LD. To read data from a file directly, you can add the `@` symbol followed by the filepath, e.g. `@/path/to/file.jsonld`.
+
 We now have the IRIs for the `metadata` field of each credit class, project, and batch.
 
 ## Data Resolvers