Add PackageReadmeFile

Author: CZEMacLeod

src/Directory.Build.Targets

@@ -23,6 +23,7 @@
     <Company>Cloud3D Ltd.</Company>
     <Copyright>©2023 Cynthia Z E Macleod All rights reserved.</Copyright>
     <PackageLicenseFile>LICENSE.txt</PackageLicenseFile>
+    <PackageReadmeFile Condition="EXISTS('$(MSBuildProjectDirectory)\README.md')">README.md</PackageReadmeFile>
     <PackageLicensePath>$(MSBuildThisFileDirectory)..\$(PackageLicenseFile)</PackageLicensePath>
     <PackageProjectUrl>https://github.com/CZEMacLeod/MSBuild.SDK.SystemWeb</PackageProjectUrl>
     <RepositoryUrl>https://github.com/CZEMacLeod/MSBuild.SDK.SystemWeb.git</RepositoryUrl>