Website: Add Open Collective as donation option (#125)
    
    Co-authored-by: 6543 <6543@obermui.de>
    Reviewed-on: https://codeberg.org/ForgeFed/ForgeFed/pulls/125
    Reviewed-by: Loïc Dachary <dachary@noreply.codeberg.org>
    Reviewed-by: Ta180m <ta180m@noreply.codeberg.org>