Update README with new audio

[tsweet64]

From #13

TODO:

• [x] Ensure that final torrent(s) results in the same number of files under statistics
• [x] Publish torrents
• [x] Update announcement date with torrent publish date
• [x] Explain the differences (original, mp3, opus)
• [x] Update pictures (読む hover, statistics)
• [x] Credits (link to preprocessing repo)
• [x] Add note at the very bottom on how to update audio (under <details> tag)
• [x] Remove known issue part with .aac files
• [x] Update sources and default URL (remove sources entirely from default URL so it'll fallback to whatever we change the default_config.json to)
• [x] Reword disadvantages (there's now a hell of a lot more coverage than standard Yomichan)

Made a new PR in order to collaborate on this branch

See here for the rendered result.