fix: added content-length header for single part uploads

What's Changed

• mention libmagic system requirement in readme by @martenson in #6
• Always send content length by @mesemus in #8
• Adding content-length for single part uploads in a sync client. by @mesemus in #9

New Contributors

• @martenson made their first contribution in #6

Full Changelog: 0.8.2...0.8.3