Add docs about emoji stealing (#364)

Add docs about emoji stealing (#364)

I managed to steal some emoji, but I had to figure out the specifics the hard way. This should make it easier for future criminals.

Feel free to close if this documentation was omitted on purpose, I can imagine some reasons for why it might have.

Co-authored-by: timorl <timorl@disroot.org>
Reviewed-on: https://akkoma.dev/AkkomaGang/akkoma/pulls/364
Co-authored-by: timorl <timorl+akkomadev@disroot.org>
Co-committed-by: timorl <timorl+akkomadev@disroot.org>