Include suggested platforms for validation

Author: dibarbet

test-plan.md

@@ -8,6 +8,11 @@
 
 See [OmniSharp Options](https://github.com/OmniSharp/omnisharp-vscode/blob/master/test-plan.md#omnisharpusemodernnet-all-platforms) for more details.
 
+### Validation
+
+#### Platforms
+All the validations below should be performed on both Windows and at least one Unix platform (MacOS, Linux)
+
 #### Opening projects
 When you open a directory in VS Code, the C# extension should look for a .csproj, .sln, or .slnf file in that directory and use "OmniSharp" to load it. If a .cs file is present and no .csproj, .sln, or .slnf file are present, Omnisharp should start but the intellisense should only appear when a change is made to the file.
 If you look in "Output > Omnisharp Log" a bunch of information should be printed about what copy of MSBuild was used and what projects were load