`include` does not work in SUMMARY.md

[nicholashaydensmith]

Problem

This is a reopening of issue #1116

I think this feature would provide the most natural way to support auto-generated documentation. One could autogen a whole tree of md's and then a snippet TOC that gets included in SUMMARY.md.

[colommar]

Hello! I have a question. Some articles in the mdbook don't have obvious signs indicating the order of the chapters, so how can I make sure that they are in order when automatically generating the README.md file? Or is random generation sufficient.

[deerchao]

This feature would be really useful.

[jplwill]

Agreed, I'd really like to see this happen.