Update _extras/guide.md

Co-authored-by: Steve Crouch <s.crouch@software.ac.uk>

Author: anenadic

_extras/guide.md

@@ -87,7 +87,7 @@ This synchronisation becomes particularly important for later workshop stages
 when students start with group exercises.
 
 ### Helpers Roles and Responsibilities
-At the workshop, "self-learning with helpers" mode everyone in the training team is a helper and 
+At the workshop, when using the "self-learning with helpers" delivery mode, everyone in the training team is a helper and 
 there are no insturctors per se.
 You may have more experienced helpers delivering introductions to the workshop and sections.
 Contact the course authors for the section intro slides you can reuse and you can also find slides for each