[xml] Support libxml2 and libxslt on Open Collective

[Nick Wellnhofer <wellnhofer aevum de>]

Hello,

You can now support libxml2 and libxslt financially on Open Collective:

    https://opencollective.com/libxml2

All donations go through the Open Source Collective, a non-profit organization 
providing financial and legal infrastructure for thousands of open source 
projects.

    https://www.oscollective.org/

If you prefer, you can also support me directly. Just get in touch by email.

Nick