Add usage page for F#

Using EF from F# requires several specific patterns that differ from C#, and wouldn't be obvious to a beginner. We should age a page summarizing those things.

* DbSet auto-initialization is not supported (because of how F# works) - people need to explicitly initialize their DbSet properties (see [#34356](https://github.com/dotnet/efcore/issues/34356)).
* Use EF.Parameter() for parameterization (see [#12841](https://github.com/dotnet/fsharp/issues/12841))
* Use the external EFCore.FSharp package, especially for migrations and scaffolding ([see discussion](https://github.com/dotnet/efcore/issues/14572#issuecomment-2314823138))