[patch] Add UsageError example for parseBlueprintOptions

[danielsharvey]

PR adds 'UsageError' handling for custom parseBlueprintOptions() errors. This is an example usage.

[sailsbot]

Hi @danielsharvey! It looks like the title of your pull request doesn’t quite match our guidelines yet. Would you please edit your pull request's title so that it begins with [proposal], [patch], [fixes #<issue number>], [implements #<other PR number>], or [misc]? Once you've edited it, I'll take another look!

[sailsbot]

Thanks for submitting this pull request, @danielsharvey! We'll look at it ASAP.

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