Add config caveats to FAQ

Author: badeball

docs/faq.md

@@ -4,6 +4,7 @@
 * [I get `fs_1.promises.rm is not a function`](#i-get-fs_1promisesrm-is-not-a-function)
 * [I get `spawn cucumber-json-formatter ENOENT`](#i-get-spawn-cucumber-json-formatter-enoent)
 * [Why is `cypress-tags` missing?](#why-is-cypress-tags-missing)
+* [My JSON report isn't generated](#my-json-report-isnt-generated)
 
 ## `--env` / `tags` isn't picked up
 
@@ -22,3 +23,7 @@ You need to install `cucumber-json-formatter` **yourself**, as per [documentatio
 From [#689](https://github.com/badeball/cypress-cucumber-preprocessor/issues/689):
 
 > The `cypress-tags` has been removed and made redundant. Specs containing no matching scenarios are [automatically filtered](https://github.com/badeball/cypress-cucumber-preprocessor/blob/master/docs/tags.md#running-a-subset-of-scenarios), provided that `filterSpecs` is set to true.
+
+## My JSON report isn't generated
+
+You have likely stumbled upon a configuration caveat, see [docs/configuration.md: Caveats / Debugging](configuration.md#caveats--debugging).