Update README.md

[sipsuru]

• Added links to download old versions of FE for linux, mac, mac-arm64.
• Added <br> to break link url, and download example.
• Edited links organization a bit.
• Corrected file names.
• Improved files names (fiddler -> fiddler.dylib)
• XXXXXXX random "x"s fixed -> 8 "X"s.
• Added information on how to change username (first & last) & email.
• Some other minor changes.