Specify markdown description in csproj file - msbuild

Question

When using dotnet pack, I can use properties like RepositoryUrl to use as the resulting .nuspec file's repository URL etc.
But what property do I set to specify markdown content? Is it even possible to specify via .csproj files?
If not, how do I do it in a .nuspec file? The documentation is very lacking. According to this link, some interns have apparently published the feature - but how do I use it?

Answer 1

Update: You can use NuspecProperties as a Semicolon separated list of key=value pairs.
Here the complete command reference for csproj, in particular you have to set the documentation property as below reference:
According to this Nuspec documentation
You can specify the property documentation
<documentation src="documentation.md" />
in your .nuspec file.
target defaults to package root
Supported formats - md
On pack, strip source value, append the target value with the source file name - <documentation target="documentation.md"/>. (this is to help the gallery and the client know the path to the documentation file in the package and the file name.extension. Allows for extension validation, etc.)
nuget spec will add
<!-- e.g. <documentation src="documentation.md"/>. Learn more at https://aka.ms/nugetPackageDocumentation-->
<documentation src=""/>
package submitted to NuGet.org - target should not be null
Sidenote: this answer comes with a documentation resource published later than when the question was asked.