[FIX] Clarify MEG empty-room recommendations

src/04-modality-specific-files/02-magnetoencephalography.md

@@ -592,7 +592,10 @@ Empty-room MEG recordings capture the environmental and recording system's
 noise.
 In the context of BIDS it is RECOMMENDED to perform an empty-room recording for
 each experimental session.
-It is RECOMMENDED to store the empty-room recording inside a subject directory
+
+If empty-room recordings are not done prior to each individual experimental session, but
+on a daily schedule, one empty-room recording may have to be used with multiple subjects and/or sessions. In that case
+it is RECOMMENDED to store the empty-room recording inside a subject directory
 named `sub-emptyroom`.
 The label for the [`task-<label>`](../99-appendices/09-entities.md#task) entity in the empty-room recording SHOULD be
 set to `noise`.
@@ -607,7 +610,7 @@ It should be possible to query empty-room recordings just like usual subject
 recordings, hence all metadata sidecar files (such as the `channels.tsv`) file
 SHOULD be present as well.
 
-Example:
+Example 1:
 
 <!-- This block generates a file tree.
 A guide for using macros can be found at
@@ -630,4 +633,29 @@ A guide for using macros can be found at
    }
 ) }}
 
+
+Example 2:
+
+<!-- This block generates a file tree.
+A guide for using macros can be found at
+ https://github.com/bids-standard/bids-specification/blob/master/macros_doc.md
+-->
+{{ MACROS___make_filetree_example(
+   {
+   "sub-control01": {
+      "ses-01": {
+         "sub-01_ses-01_scans.tsv": "",
+         "meg": {
+            "sub-control01_ses-01_task-rest_meg.ds": "",
+            "sub-control01_ses-01_task-rest_meg.json": "",
+            "sub-control01_ses-01_task-rest_channels.tsv": "",
+            "sub-control01_ses-01_task-noise_meg.ds": "",
+            "sub-control01_ses-01_task-noise_meg.json": "",
+            "sub-control01_ses-01_task-noise_channels.tsv": "",
+            }
+         }
+      },
+   }
+) }}
+
 <!-- Link Definitions -->