Clarify instructions to obtain a token right from the app

[oguzgelal]

https://community.wanikani.com/t/ios-android-web-juken-review-app-for-wanikani/43841/52

[Anonakorok]

Assuming that this might manifest in something like a help article on the home page when first setting up the app, I might add: also be sure to clarify the error warning when the app fails to push review status back to Wanikani to mention that you might want to double check whether you granted review access with your API token. (Since folks may skip past the help when setting up the app and then find themselves stuck later. You know how it is with humans and choosing to read the fine print...)

Currently, this requirement wasn't mentioned in the popup you can view when uploads fail, only a suggestion that you retry or ignore the error (I believe), so it took me a while to figure out that the lack of the correct rights being granted was what was causing my issue with uploading my reviews. I nearly gave up on the app, so a bit more handholding for new users could help keep retain users. Great work on the app so far!