add this missing FSIStrings Embedded Resource

[baronfel]

@matthid This should add the resource back in.

[dsyme]

Looking at the OSX build, we annoyingly seem to be getting duplicate resources.

 --resource:obj/Release/FSComp.resources
--resource:obj/Release/FSIstrings.resources
--resource:obj/Release/FSComp.resources
--resource:obj/Release/FSIstrings.resources

I haven't yet determined why - duplicates aren't appearing when the same FSharp.Compiler.Tools targets file is being used in the fsharp/fsharp builds. Very strange to have this problem back.

[dsyme]

This change itself is good, so I will merge this, but we need to get to the bottom of why the duplicates are happening

[matthid]

Thanks for this :)