[FIX] run entity - "scans" -> "data samples"

As we have now other modalities, such as EEG and MEG, "scan" is not really the
most appropriate term here.  Having said that we do use _scans etc for EEG and
MEG as well ATM, as it was the "forward compatible" with existing MRI centric
BIDS back then.

src/schema/entities.yaml

@@ -85,7 +85,7 @@ run:
   name: Run
   entity: run
   description: |
-    If several scans with the same acquisition parameters are acquired in the same session,
+    If several data samples (e.g., MRI scans) with the same acquisition parameters are acquired in the same session,
     they MUST be indexed with the [`run-<index>`](../99-appendices/09-entities.md#run) entity:
     `_run-1`, `_run-2`, `_run-3`, and so on (only nonnegative integers are allowed as
     run labels).