Add note about routing with special characters not working in .net core, 5+

[Nils-Berghs]

Routing in .net (starting with core and at least up to 7) does not work for strings, nor is there a workaround possible.
The problem is that route parameters are half URL decoded by the middleware (Yes halve). So unless you know in advance what all possible routing values will be, routing WILL NOT and CAN NOT reliably work.

see dotnet/aspnetcore#11544

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Document Details

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• ID: 8ee6ad2f-1667-8d5c-1f36-9d0511e3720f
• Version Independent ID: 7838ccec-c8e8-9baa-2b3e-220b2af5fc58
• Content: Routing to controller actions in ASP.NET Core
• Content Source: aspnetcore/mvc/controllers/routing.md
• Product: aspnet-core
• Technology: aspnetcore-mvc
• GitHub Login: @Rick-Anderson
• Microsoft Alias: riande

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Associated WorkItem - 60876

[Rick-Anderson]

Routing works with most strings, just not special characters like / which is a route separator. Routing works with valid URI characters.