clarify docs

Author: emiglietta

documentation/DCP-documentation/step_2_submit_jobs.md

@@ -100,6 +100,8 @@ Separate values with commas and no spaces and surround with quotation marks (e.g
 Formats wells passed with `--plate format` or `--rows` and `--columns` but not `--wells`.
 (e.g. `A1` NOT `A01`)
 * `--sites <value>`: a custom list of sites (fields of view) to be analyzed.
+Default is 9 sites (1 to 9).
+Not used by `illum`, `qc`, or `assaydev` steps.
 Separate values with commas and no spaces and surround with quotation marks (e.g. `"1,2,3,4,5,6"`)
 
 ### Overwrite structural defaults