[DOCS] provide guidance on MetadataViews in HybridCustody

[sisyphusSmiling]

Related: #16

It was noted in the audit report that it was not possible to update ProxyAccount.display as the parent account since ProxyAccount.setDisplay() is access(contract). However, this functionality is enabled by Manager.setChildDisplay().

This misconception highlights the need for better documentation on this fact. Any documentation should cover the displays for both ChildAccount and ProxyAccount, who can change each, when in the linking process each should be set, which resource to rely on as source of truth, and how to resolve this.

Other topics to note might include warning about phishing vectors, and how to add additional view types via data buckets.