Updated guide

README.md

@@ -22,7 +22,8 @@ Input fields top down:
 1. _Study Base folder:_
    Selects the study folder. The study folder is the folder, which contains the subject folders.
 2. _Subject prefix:_
-   If the subject folders of the selected study use a different prefix than "sub-", enter their prefix here.   
+   If the subject folders of the selected study use a different prefix than "sub-", click the checkbox and enter their prefix here.
+   If the subject folders contain no shared prefix, type "." in the input field to treat all folders inside the selected study as subject. If a selected folder does not contain any subject data, errors for this folder may be ignored.
 3. _Submit_:
    Starts performing checks on the given study.