Update Pull Request template

* Add note about package ownership for new providers.
* Add note that creating issues for pull requests is optional.

Author: martincostello

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,5 +1,16 @@
-_Summarize the changes this Pull Request makes._
+<!--
 
-_If adding a new provider, please ensure you have included appropriate test(s)._
+Summarize the changes this Pull Request makes.
 
-_Please include a reference to a GitHub issue if appropriate._
+Please include a reference to a GitHub issue if appropriate.
+It is not necessary to create a new issue just to open a Pull Request.
+
+If adding a new provider, please ensure you have included appropriate test(s).
+
+For new providers, a package with the same ID must not already exist in NuGet.org.
+If it does, you must be the owner of the package and agree to transfer ownership
+of the package to the [aspnet-contrib](https://www.nuget.org/profiles/aspnet-contrib)
+organisation after the Pull Request is merged so we can take over publishing of
+the provider from our Continuous Integration.
+
+-->