change outdated link to doc

docs/README.md

@@ -44,7 +44,7 @@ You most likely want to make changes to the files in the folder `en`. That's
 where all the real documentation text is located. The documentation is written
 in reStructuredText, a simple syntax to structure the text. You can find
 information about it in the [reStructuredText
-Primer](http://sphinx-doc.org/rest.html) or by looking at what is already in
+Primer](https://sublime-and-sphinx-guide.readthedocs.io/en/latest/topics.html) or by looking at what is already in
 the documentation and make your changes according to it.
 
 Once you have made changes which you would like to contribute back to the main