Fix wrong version specification in hidi examples in readme.md

[Expecho]

The examples show a wrong value for specifying the OpenApi version. Using the examples I got this error:

crit: Microsoft.OpenApi.Hidi.Handlers.TransformCommandHandler[0]
Could not transform the document, reason: Invalid version format. Please provide a valid OpenAPI version (e.g., 2.0, 3.0, 3.1).
PS Z:\Sources\dotnet10\ai> hidi transform -d .\openapi.yaml -f yaml -o .\openapi-trimmed.yaml -v OpenApi3_0 --op users.user.calendar.getSchedule,places.place.ListPlace.AsRoom --co

It took me a while before I figured out I need to use the major minor syntax, so -v OpenApi3_0 must be changed to -v 3.0 to get the examples working.

[baywet]

Thanks for the contribution!