Add information about summary format

1 files changed, 25 insertions, 0 deletions

diff --git a/README.md b/README.md
index 6d37943..9a87f38 100644
--- a/README.md
+++ b/README.md
@@ -30,3 +30,28 @@ Options for commands `build` and `serve` are:
 -i, --intro <intro> Description of the book to generate
 -g, --github <repo_path> ID of github repo like : username/repo
 ```
+
+## Book Format
+
+A book is a GitHub repository containing at least 2 files: `README.md` and `SUMMARY.md`.
+
+#### SUMMARY.md
+
+The SUMMARY.md is used for getting the complete summary of the book. It should contains a list of items (deep items are allowed) with links to the different pages.
+
+Example:
+
+```
+# Summary
+
+This is the summary of my book.
+
+* [section 1](section1/README.md)
+    * [example 1](section1/example1.md)
+    * [example 2](section1/example2.md)
+* [section 2](section2/README.md)
+    * [example 1](section2/example1.md)
+```
+
+All the other content than the summary list will be ignored.
+