[FIX] Clarify use of session entity in file names (#532)

* Clarify when ses-<label> is optional

Clarify that the ses-<label> entity is REQUIRED in file names when the session level is present in the folder structure.

* Clarify when ses-<label> is optional

Update to the entity table.
It's actually required in some cases, and not to be used in others.  It's never really optional...

* Update 01-contributors.md

* Revert changes to entity table.

This reverts commit 7708479.

* Update src/02-common-principles.md

Co-authored-by: Chris Markiewicz <[email protected]>

Co-authored-by: Chris Markiewicz <[email protected]>

Author: Moo-Marc

src/02-common-principles.md

@@ -99,7 +99,9 @@ A file name consists of a chain of *entities*, or key-value pairs, a *suffix* an
 Two prominent examples of entities are `subject` and `session`.
 
 For a data file that was collected in a given `session` from a given
-`subject`, the file name will begin with the string `sub-<label>_ses-<label>`.
+`subject`, the file name MUST begin with the string `sub-<label>_ses-<label>`. 
+If the `session` level is omitted in the folder structure, the file name MUST begin 
+with the string `sub-<label>`, without `ses-<label>`.
 
 Note that `sub-<label>` corresponds to the `subject` entity because it has
 the `sub-` "key" and`<label>` "value", where `<label>` would in a real data file

src/99-appendices/01-contributors.md

@@ -92,6 +92,7 @@ your name is not listed, please add it.
 -   Gregory Kiar 📖💻🎨🔧
 -   Robert Knight 📖
 -   Jean-Philippe Lachaux 📖
+-   Marc Lalancette 📖
 -   Pamela LaMontagne 📖💡
 -   Kevin Larcher 💬
 -   Jonathan C. Lau 📖