Add paket.template "readme" file support.

[seanamos]

This is another step towards closing #3710

Nuget added the ability to specify a path to a readme file within your package that will be displayed on nuget.org.
This adds the readme field to paket.template.

[seanamos]

Checking the failing test, it doesn't seem related to any changes I've made.

The relevant failure output:

ERR:-> Request to 'https://www.myget.org/F/dotnet-core-svc/api/v3/index.json' failed with unknown error (_safeGetFromUrl)
ERR:-> HttpRequestException: An error occurred while sending the request.
ERR:   StackTrace:
ERR:        at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
ERR:        at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
ERR:        at System.Net.Http.HttpClient.<FinishSendAsyncBuffered>d__58.MoveNext()
ERR:-> WinHttpException: Error 12175 calling WINHTTP_CALLBACK_STATUS_REQUEST_ERROR, 'A security error occurred'.
ERR:   StackTrace:
ERR:        at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
ERR:        at System.Threading.Tasks.RendezvousAwaitable`1.GetResult()
ERR:        at System.Net.Http.WinHttpHandler.<StartRequestAsync>d__109.MoveNext()
  Stack Trace:

Visiting https://www.myget.org/F/dotnet-core-svc/api/v3/index.json , it does look like there is a certificate problem which results in the test failing.

[baronfel]

Yep, you're right. That test has been failing on all PRs lately but you've done the first root cause on it.

[seanamos]

Some very quick digging and it looks like dotnet.myget.org has been deprecated.

https://docs.microsoft.com/en-us/answers/questions/337663/invalid-certificate-for-mygetorg.html

So the question is then, what to do with the test? Can we just remove it?

[baronfel]

The failing test issue should be unblocked/fixed by #4042