[lang] Update Goodreads API key instructions (#6542)
[lang] Update Goodreads API key instructions (#6542)

Closes <https://github.com/koreader/koreader/issues/6539>.
Hzj-jie/koreader,mwoz123/koreader,pazos/koreader,NiLuJe/koreader,koreader/koreader,Frenzie/koreader,koreader/koreader,NiLuJe/koreader,Frenzie/koreader,poire-z/koreader,Markismus/koreader,poire-z/koreader