Add slight clarification about IsTrimmable metadata (#42317)

Author: sbomer

docs/core/deploying/trimming/trimming-options.md

@@ -27,7 +27,7 @@ Place this setting in the project file to ensure that the setting applies during
 
 :::zone pivot="dotnet-8-0,dotnet-7-0"
 
-This setting enables trimming and trims all assemblies by default. In .NET 6, only assemblies that opted-in to trimming via `[AssemblyMetadata("IsTrimmable", "True")]` were trimmed by default. You can return to the previous behavior by using `<TrimMode>partial</TrimMode>`.
+This setting enables trimming and trims all assemblies by default. In .NET 6, only assemblies that opted-in to trimming via `[AssemblyMetadata("IsTrimmable", "True")]` (added in projects that set `<IsTrimmable>true</IsTrimmable>`) were trimmed by default. You can return to the previous behavior by using `<TrimMode>partial</TrimMode>`.
 
 :::zone-end