Please add the Sparkplug membership prospectus in the banner section on sparkplug.eclipse.org

Created by: Ioana240

The goal is to add the Sparkplug membership prospectus in the banner section on sparkplug.eclipse.org

1. Go to https://sparkplug.eclipse.org/
2. In the banner section, add a button on the right side similar to "Join us on Slack" button, see screenshot
3. Add the membership prospectus to the button, link here: https://www.eclipse.org/membership/documents/sparkplug-membership-prospectus.pdf

Thank you!