Expand on Capability configuration required for account linking

Description

A recent question in Discord reveals a lack of docs coverage on configuring child account NFT collections for access from a parent account. This same question has been raised at least one other time in Discord.

The two account linking guides should be updated with a section or a callout covering the use of Capabilities. A dropdown section and diagram with an explainer on how Capabilities are leveraged to facilitate accessing assets from child accounts would also be helpful for conceptual understanding.

Guidance should cover the fact that child account collections should be configured to include the issuance of a Capability ( e.g. auth(NonFungibleToken.Withdraw) &{ExampleNFT.ExampleNFTCollectionPublic, NonFungibleToken.CollectionPublic, NonFungibleToken.Provider} as shown here) so a CapabilityController can be accessed via the parent account.

It should also be noted that this Capability should not be published, simply issued during setup. An explicit reference to the error they might encounter if they don't complete this step would also be helpful - [Error Code: 1101] cadence runtime error: Execution failed: error: panic: no controller found for capType.

Locate the two account linking guides and review the linked setup_full.cdc example for the Capability configuration context. Update the guides with the requested explanation, callout or dropdown, diagram, issuance-versus-publication guidance, and error reference; the work is done when child-account collection setup and parent-account access are understandable without Discord context.