Update "How Tor Works" diagram

@nicob created new onion routing diagrams (tpo/community/outreach#40065 (comment 3044306)) and are available in Nextcloud.

Let's replace the old illustration https://tb-manual.torproject.org/about/ with the new diagram (probably need some resize):

We will need to update this phrase:"The image above illustrates a user browsing to different websites over Tor. The green middle computers represent relays in the Tor network, while the three keys represent the layers of encryption between the user and each relay."