Update part0a.md

Possible small typo in the section "How to study the course – instructions in a nutshell: other course parts".

When it reads "... marking them is done on the submission system".

We assume that it meant to say "... marking them as done on the submission system"

Author: GMarindev

src/content/0/en/part0a.md

@@ -186,7 +186,7 @@ Please note that if you do the "base course" with 6 or 7 credits, you need separ
 
 How to study the course – instructions in a nutshell: other course parts
 
-- Do the exercises. The exercises are submitted through GitHub and marking them is done on the submission system. Note that parts 8-13 have a separate instance in the submission system
+- Do the exercises. The exercises are submitted through GitHub and marking them as done on the submission system. Note that parts 8-13 have a separate instance in the submission system
     - [The course certificate](/en/part0/general_info#course-certificate) will be available in the submission system
 - If you want to get University of Helsinki credits
     - Enroll in the course. You can enroll in each part through the link in the course material ([Parts and completion](/en/part0/general_info#parts-and-completion)). Enroll in each part separately.