Create a new section about Tor Browser anti-fingerprinting features

While discussing with @ebanam about adding letterboxing on TB manual, we realized that we don't have an explanation about all the anti-fingerprinting features developed and available on Tor Browser, which is a piece of software way more complex than "Firefox with Tor".

@richard and TB Team is updating TB design doc: tpo/applications/wiki!1 (merged), although it's not ready, we can definitely pick some of these features for this new section.

I think this section will address many common user questions (https://forum.torproject.org/tag/fingerprinting).

Tasks

• Create a new section in main: "Anti-fingerprinting"
• Write an introduction about fingerprinting, mention these previous blog posts: https://blog.torproject.org/browser-fingerprinting-introduction-and-challenges-ahead/ https://blog.torproject.org/tor-browser-advancing-privacy-innovation/
• Add letterboxing explanation