Add a note about loading multiple properties for Entry

this works:
`await context.Entry(ent).Reference(o => o.Prop1).LoadAsync();`
but how do you load multiple properties, you can't chain multiple `.Reference`

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#### Document Details

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* ID: cc261727-1ecd-5dcb-fb88-1b1762263789
* Version Independent ID: a15c2f82-ebb7-9867-50ad-35f80366528f
* Content: [Explicit Loading of Related Data - EF Core](https://docs.microsoft.com/en-us/ef/core/querying/related-data/explicit)
* Content Source: [entity-framework/core/querying/related-data/explicit.md](https://github.com/dotnet/EntityFramework.Docs/blob/main/entity-framework/core/querying/related-data/explicit.md)
* Product: **entity-framework**
* Technology: **entity-framework-core**
* GitHub Login: @roji
* Microsoft Alias: **avickers**