Here are a few examples from projects that have adapted this work.
The BeeWare Project, a collection of projects used to develop, debug, and launch Python software, was the first to adopt the imposter syndrome disclaimer in their excellent documentation for first-time contributors. Their resource covers the disclaimer, how to help, using GitHub, setting up the environment, common questions, and other first-timer friendly resources. Definitely check it out if you're developing your own guide!
Netflix's Cloud Security team released Diffy: a differencing engine for digital forensics in the cloud, in July 2018. (Announcement on their tech blog) They're using this Imposter Syndrome Disclaimer in their Contributing Guide.