build(release): add package icon for the nuget package (#29)

Closes #28

Author: hamzamahmood

APIMatic.Core/APIMatic.Core.csproj

@@ -20,11 +20,13 @@
         <PackageTags>APIMatic;dotnet;core;Core Library</PackageTags>
         <PackageProjectUrl>https://www.apimatic.io</PackageProjectUrl>
         <GeneratePackageOnBuild>True</GeneratePackageOnBuild>
+        <PackageIcon>icon.png</PackageIcon>
     </PropertyGroup>
 
     <ItemGroup>
         <None Include="..\LICENSE" Pack="true" PackagePath="" />
         <None Include="..\README.md" Pack="true" PackagePath="\" />
+        <None Include="icon.png" Pack="true" PackagePath="\" />
     </ItemGroup>
 
     <ItemGroup>