Clarify that callouts are optional

This came up in my teaching demo this morning and has come up in several demos before. Trainees were surprised that callouts weren't a required part of the lesson. They were trying to teach all of the callouts, which is a timing problem, especially for some of the older SWC lessons where there are many callouts. It would be good to emphasize somewhere in training and/or documentation that callouts are optional extras that Instructors can include or skip depending on time, the questions that learners are asking, and interest in particular topics.

Review the instructor training and documentation areas to find where callouts are introduced. Update the relevant guidance so it states that callouts are optional and may be included or skipped based on time, learner questions, and topic interest. Done means instructors are unlikely to mistake callouts for required lesson content.

Written by the indexing model from the issue text.