Explain how to take screenshots in Tails

Applications → Accessories → Screenshot

I’m not sure whether this deserves a full page in “Sensitive documents” but at least it needs to appear or be linked from the bug reporting instructions.

Parent Task: #8660

Related issues

Related to #12723 (closed)
Blocks #16711

Original created by @sajolida on 8666 (Redmine)

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information