Update .NET README prerequisites

Move the .NET README requirements section above installation, rename it to prerequisites, and clarify the runtime requirement as any .NET Standard 2.0-compatible implementation.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: scottaddie

dotnet/README.md

@@ -2,6 +2,11 @@
 
 SDK for programmatic control of GitHub Copilot CLI.
 
+## Prerequisites
+
+- Any of the [.NET Standard 2.0-compatible .NET implementations](https://learn.microsoft.com/dotnet/standard/net-standard?tabs=net-standard-2-0#select-net-standard-version)
+- GitHub Copilot CLI installed and in PATH (or provide custom `Connection = RuntimeConnection.ForStdio(path: ...)`)
+
 ## Installation
 
 ```bash
@@ -982,11 +987,6 @@ catch (Exception ex)
 }
 ```
 
-## Requirements
-
-- .NET 8.0 or later
-- GitHub Copilot CLI installed and in PATH (or provide custom `Connection = RuntimeConnection.ForStdio(path: ...)`)
-
 ## License
 
 MIT