Updated C# and .NET docs supplement (markdown)

C#-and-.NET-docs-supplement.md

@@ -1,5 +1,5 @@
 To save us repeating our complaints about the lack of proper documentation under each section, let's agree to gather all the frustration here:
-> AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
+> AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
 
 Contribute to [the official docs](https://github.com/dotnet/docs) if possible.
 
@@ -32,6 +32,11 @@ Use `MSBuildProjectDirectory`. Note that the latter doesn't include a trailing s
 
 `dotnet list BizHawk.sln package --outdated` will list outdated `<PackageReference/>`s
 
+## NUL-terminated strings
+
+.NET will happily include NUL (`(char) 0`) in a string if you use `String..ctor(char[])`.
+WinForms' `Label.Text` stops reading at the first NUL for measurement/rendering, at least under Mono.
+
 ## `String.GetHashCode` stability
 
 The `GetHashCode` implementation for strings does not reflect the string's contents, and as such, the hash not stable between program instances.