https://powerapps.microsoft.com/en-us/blog/custom-form-launch/
enabling support for multi-value choice, lookup, and person column types, and read-only support for attachments in PowerApps.
Note: These changes are rolling out incrementally for SharePoint First Release tenants and are not generally available from SharePoint yet. So, if your tenant is already on first release, you should already have them and if your tenant is not on first release, to enroll please follow the instructions here.