update directory build props (#117)

Author: phnx47-bot

Directory.Build.props

@@ -4,4 +4,13 @@
     <IsPackable>false</IsPackable>
     <NoWarn>CS1591;NETSDK1138</NoWarn>
   </PropertyGroup>
+  <PropertyGroup Condition="'$(GITHUB_ACTIONS)' == 'true'">
+    <ContinuousIntegrationBuild>true</ContinuousIntegrationBuild>
+  </PropertyGroup>
+  <ItemGroup>
+    <PackageReference Include="Microsoft.SourceLink.GitHub" Version="8.0.0">
+      <PrivateAssets>all</PrivateAssets>
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers</IncludeAssets>
+    </PackageReference>
+  </ItemGroup>
 </Project>