Introduce teacher documentation for annotations

[jorg-vr]

This adds an faq about questions and comments

This faq was made in the context of the release of saved annotations: dodona-edu/dodona#4992

[bmesuere]

@jorg-vr I propose rewriting it to these questions

# Questions and comments

## How can I ask a question about my code? <Badge type="tip" text="student" />

(also add an info box that questions might be disabled)

## How do I know if my question has been answered? <Badge type="tip" text="student" />

## How can I enable/disable student questions? <Badge type="tip" text="teacher" />

## How do I know if there are any open questions? <Badge type="tip" text="teacher" />

## How can I reply to a question from a student? <Badge type="tip" text="teacher" />

## How can I comment on a students' submission? <Badge type="tip" text="teacher" />

## How can I store and reuse comments? <Badge type="tip" text="teacher" />

[bmesuere]

This would also close #169. There is some content in the issue there that could be used here.