Migrate `adapt-and-extend/theming/resourceregistry`

[stevepiercy]

Plone Documentation versions affected

• 5.x
• 6.x

Description

Source

https://github.com/plone/documentation/blob/5.2-myst/5.2-myst/adapt-and-extend/theming/resourceregistry.md

Rendered

https://docs.plone.org/adapt-and-extend/theming/resourceregistry.html

Update links

backend/upgrading/version-specific-migration/p4x-to-p5x-upgrade.md