jenkins-infra/helm-chartsand I am extremely humbled to see the helping nature and openness of the community. Thanks a lot to all for establishing an open source project of this grandeur!
Pipeline Step Documentation Generator improvementsand also find the
Plugin Health Scoring systemidea interesting. Thank you.
I recommend that you start with https://www.jenkins.io/doc/developer/
More specific to Jelly, you have https://www.jenkins.io/doc/developer/forms/jelly-form-controls/
The how-to's might also help you to get started.