chore(docs): Clarify failOn setting

[LekoArts]

Description

Clarification to the failOn setting coming from the discussion in #3480. Goal of this PR is to set correct expectations of when failOn is actually applied internally and which images are always expected to fail regardless of the setting of this

Related Issues

Fixes #3480

[lovell]

Thank you very much for the PR, how about something like:

when to abort processing of invalid pixel data, one of (in order of sensitivity): 'none' (least), 'truncated', 'error' or 'warning' (most), higher levels imply lower levels, invalid metadata will always abort

Please can you update the JSDocs then use npm run docs-build to automagically update the markdown.

sharp/lib/constructor.js

Line 122 in 2a71f18

* @param {string} [options.failOn='warning'] - level of sensitivity to invalid images, one of (in order of sensitivity): 'none' (least), 'truncated', 'error' or 'warning' (most), highers level imply lower levels.

[LekoArts]

Done 👍

[lovell]

Brilliant, thank you.