add mapping for Rev_News files and link to the usual draft

The Git Rev News web pages are not an immediately obvious
mapping to the archive posts directory. Spell it out.

Also add a link to the usual draft directory to help light reading
contributors who maybe using GitHub's web interface.

Author: PhilipOakley

rev_news/rev_news.md

@@ -21,14 +21,20 @@ Subscribe to Git Rev News by [RSS/atom](https://git.github.io/feed.xml) or by si
 
 You can find a listing of all previous editions on the [Git Rev News Archive](https://git.github.io/rev_news/archive/) page.
 
+The web page is autogenerated based on the files stored in the `_posts` directory.
+The basic mapping is edition https://git.github.io/rev_news/YYYY/MM/DD/edition-NN/
+will be found in repo at
+https://github.com/git/git.github.io/blob/master/_posts/YYYY-MM-DD-edition-NN.markdown
+
 ## Contribute
 
 You can contribute to the upcoming edition by sending [pull requests](https://github.com/git/git.github.io/pulls)
 or opening [issues](https://github.com/git/git.github.io/issues).
 
 There is usually an issue opened for the upcoming edition. This issue
 should have near its top a link to a sometimes very rough draft of the
-upcoming edition.
+upcoming edition. The draft for the next edition is usually
+[here](https://github.com/git/git.github.io/tree/master/rev_news/drafts)
 
 Don't hesitate to use the `edit` button that looks like a pen to edit
 this draft and to change whatever you want. When you are done, you