Change "We do not use slides in our lessons" to indicate that slides may be used along with (not replacing) live coding

### How could the content be improved?

I know the topic of slides has been debated thoroughly (e.g, #680, #804, #1000, probably others I'm missing) but I do think this language needs to change. We just discussed in trainer training with @ErinBecker that the policy is not "do not use slides at all", but rather "use live coding". Slides may be included as a tool but should not take the place of live coding. The current language in the Instructor Training curriculum is misleading.

### Which part of the content does your suggestion apply to?

https://github.com/carpentries/instructor-training/blob/57e4eda09d81b50f0b5b010ffb2d657098218386/episodes/17-live.md?plain=1#L31

Read episodes/17-live.md around line 31 and review the linked discussion issues for the settled policy. Update the wording so it says slides may accompany live coding but must not replace it, then check that the surrounding Instructor Training curriculum remains consistent.

Written by the indexing model from the issue text.