Update SOS readme install instructions (#51181)

src/coreclr/ToolBox/SOS/SOS_README.md

@@ -2,4 +2,4 @@ SOS and other diagnostic tools now ship out of band and work with any version of
 
 SOS has moved to the diagnostics repo here: https://github.com/dotnet/diagnostics.git.
 
-Instructions to install SOS: https://github.com/dotnet/diagnostics#installing-sos.
+Instructions to install SOS: https://docs.microsoft.com/dotnet/core/diagnostics/dotnet-sos