update onboarding slides for evidence

[emilia-friedberg]

WHAT

Update the onboarding slides for Evidence.

WHY

We are now grading Evidence activities, so the old ones were inaccurate.

HOW

Just copy changes/CSS/image replacement.

Screenshots

Notion Card Links

https://www.notion.so/quill/Evidence-Scoring-Part-5-Turn-on-the-Activity-Results-Page-for-Students-d3b7675f7a61494289901afb47e75a54?pvs=4

What have you done to QA this feature?

Looked at the pages locally

PR Checklist	Your Answer
Have you added and/or updated tests?	YES
Have you deployed to Staging?	NO - going to have Jack and Jamie test everything at once
Self-Review: Have you done an initial self-review of the code below on Github?	YES