Ensure a symbols package is generated

As part of our build process, we ensure that a separate symbols package is generated. As such, this doesn't technically need to be repeated here. But as this is a best practice and one we want to enforce, we're making sure this is explicit.

Author: JeremyCaney

Directory.Build.props

@@ -15,6 +15,7 @@
     <PackageProjectUrl>https://github.com/Ignia/Topics-Library</PackageProjectUrl>
     <UseFullSemVerForNuGet>true</UseFullSemVerForNuGet>
     <NeutralLanguage>en</NeutralLanguage>
+    <IncludeSymbols>true</IncludeSymbols>
   </PropertyGroup>
 
 </Project>