Refine documentation for STAC render extension support in the Resource Administration UI

[j08lue]

Contributes to

• UI: Add support for render extension in the STAC Admin [#2317] #38

Acceptance criteria

• Described the software architecture that will enable support for editing metadata in the STAC render extension

[j08lue]

Render extension support implemented in developmentseed/stac-manager#18

No specific software architecture required.