add @teacher{} notes re: FAs to lessons

[retabak]

( pending approval of histograms lesson from @schanzer )

• [x] histograms
• [x] box plots
• [x] threats
• [x] regression

[retabak]

@schanzer and @flannery-denny -

I'm done integrating the formative assessments into the lesson plans. @flannery-denny - can you check out the branch and review the updates I've made? Would love a second pair of eyes before we merge this.

[flannery-denny]

@retabak could you please open a pull request so that I can see the differential?

[retabak]

Done. Closing this issue, as I think we can have any further conversation about this issue via comments on the PR.