Provide fragment template in changelog.d/README

[brettcannon]

While it's neat that fragments can provide entries across multiple categories, it does mean the files do have a specific structure. Because of that you can't easily create a fragment from scratch in the GitHub UI if you happen to forget the fragment. Having a copy of the template that scriv create would make would be handy in such a situation.

[nedbat]

I'm not sure what the request is here. Scriv doesn't create changelog.d/README.

[brettcannon]

It's an ask for this repo specifically to put a copy of fragment template that users are expected to edit in https://github.com/nedbat/scriv/blob/master/changelog.d/README.txt as an example. For instance, while I was reading the docs I couldn't find an example of what a fragment that the user will end up editing looks like. And since I have found it helpful in some of my other repos to have an example entry to copy-and-paste into a new fragment file via the GitHub UI, I figured this provided an opportunity to solve two things. 😁

[webknjaz]

@nedbat look here: https://github.com/webknjaz/setuptools/tree/docs/changelog-fragments/changelog.d#readme. There's README.rst present and so GitHub renders its contents below the file/dir list. It's useful as a place for instructions for people who just navigate there and try to figure out what to do next.