Update README with new audio

[Aquafina-water-bottle]

TODO:

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