build: Create XML documentation file on "Release" build and copy it to both binary output directories (#442)

Author: Beautyod

src/Appium.Net/Appium.Net.csproj

@@ -29,7 +29,14 @@
     <FileVersion>4.2.0</FileVersion>
   </PropertyGroup>
 
-  <ItemGroup>
+  <PropertyGroup Condition="'$(Configuration)|$(TargetFramework)|$(Platform)'=='Release|netstandard2.0|AnyCPU'">
+    <DocumentationFile>Appium.Net.xml</DocumentationFile>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)|$(TargetFramework)|$(Platform)'=='Release|net45|AnyCPU'">
+    <DocumentationFile>Appium.Net.xml</DocumentationFile>
+  </PropertyGroup>
+
+	<ItemGroup>
     <None Include="LICENSE.txt" Pack="true" PackagePath="" />
   </ItemGroup>