remove 400 - Bad Request FAQ

[maryamsulemani97]

part of #1593

Moves content from the 400 - Bad Request FAQ to Core concepts/Documents

[guimachiavelli]

I think @dichotommy's suggestion that this is probably longer than it should is relevant. That FAQ answer also focusses too much on commas, when malformed JSON occurs because of many other things (missing quotes around a key, mismatched [] and {}, etc). If we simplify the text and remove the examples and the tip, it could easily fit into either Core Concepts or the Errors page without looking out place. It could even be adequate to mention it in both pages, actually, if we're ok with minor content duplication.

Out of scope, but it is interesting that you mention troubleshooting, as that is something I was reading about on Docs for Devs. To keep things short, the authors recommend having a troubleshooting reference with instructions on how to fix common errors. Not 100% how that would work, especially from an IA perspective, but could be interesting to discuss.

[maryamsulemani97]

bors merge

[bors[bot]]

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