Warn about sbt git confusion

week1/02-grading-and-submission.md

@@ -37,6 +37,10 @@ haven't committed by writing:
 git status
 ```
 
+(If you get the error `Not a valid command: git`, it means you're inside `sbt`,
+you can't run git from sbt itself, you need to open another terminal in the same
+directory)
+
 This will display the list of files you have modified since the last commit, to
 see the exact changes you made, run:
 ```shell