Add missing accepted credentials object snippet

docs/references/protocol/transactions/types/permissioneddomainset.md

@@ -40,6 +40,8 @@ _(Requires the [PermissionedDomains amendment][] {% not-enabled /%})_
 | `DomainID`            | String - [Hash][] | Hash256           | No        | The ledger entry ID of an existing permissioned domain to modify. If omitted, creates a new permissioned domain. |
 | `AcceptedCredentials` | Array             | Array             | Yes       | A list of 1 to 10 [**Accepted Credentials objects**](#accepted-credentials-objects) that grant access to this domain. The list does not need to be sorted, but it cannot contain duplicates. When modifying an existing domain, this list replaces the existing list. |
 
+### AcceptedCredentials Objects
+
 {% raw-partial file="/docs/_snippets/accepted-credentials-objects.md" /%}
 
 ## {% $frontmatter.seo.title %} Flags