[horde] Documentation on Horde/composer

[Horst Simon]

Thanks Ralf for providing more information on how to use composer!
The documentation is very helpful. I am experimenting on openSUSE Leap 15.4 with php version 8.0.10.
I have successful installed core, imp and kronolith with authentication using imp.

When a user logs on to and clicks on mail attached error is displayed, after reloading the page mail is displayed correct.

Should we report errors for Horde6, since it is still in the development stage, or wait for a more stable version.

Regards,
Horst