Remove donations section

Author: mwilliamson

README.md

@@ -613,10 +613,3 @@ are currently missing:
 * Writing embedded style maps
 * Markdown support
 * Document transforms
-
-## Donations
-
-If you'd like to say thanks, feel free to [make a donation through Ko-fi](https://ko-fi.com/S6S01MG20).
-
-If you use Mammoth as part of your business,
-please consider supporting the ongoing maintenance of Mammoth by [making a weekly donation through Liberapay](https://liberapay.com/mwilliamson/donate).