Update readme credits

Author: kepano

README.md

@@ -34,7 +34,8 @@ This plugin relies on important contributions:
 - [@akosbalasko](https://github.com/akosbalasko) for Evernote import via [Yarle](https://github.com/akosbalasko/yarle) (MIT)
 - [@daledesilva](https://github.com/daledesilva) for Google Keep import
 - [@arthurtyukayev](https://github.com/arthurtyukayev) for Bear import
-- [@joshuatazrein](https://github.com/joshuatazrein) for Notion import
+- [@xheldon](https://github.com/Xheldon) for Notion API import
+- [@joshuatazrein](https://github.com/joshuatazrein) for Notion file-based import
 - [@polyipseity](https://github.com/polyipseity) for HTML attachments
 - [@8bitgentleman](https://github.com/8bitgentleman) for Roam import
 - [@p3rid0t](https://github.com/p3rid0t) for Microsoft OneNote import