add sourceLink support (#896)

Directory.Build.props

@@ -0,0 +1,14 @@
+<Project>
+  <PropertyGroup>
+    <RepositoryType>git</RepositoryType>
+    <RepositoryUrl>https://github.com/ThreeMammals/Ocelot</RepositoryUrl>
+    <!-- Optional: Publish the repository URL in the built .nupkg (in the NuSpec <Repository> element) -->
+    <PublishRepositoryUrl>true</PublishRepositoryUrl>
+    <!-- Optional: Build symbol package (.snupkg) to distribute the PDB containing Source Link -->
+    <IncludeSymbols>true</IncludeSymbols>
+    <SymbolPackageFormat>snupkg</SymbolPackageFormat>
+  </PropertyGroup>
+  <ItemGroup>
+    <PackageReference Include="Microsoft.SourceLink.GitHub" Version="1.0.0-beta2-18618-05" PrivateAssets="All"/>
+  </ItemGroup>
+</Project>