Another reorg using summary file

.gitbook.yaml

-root: ./doc/
-
-structure:
-  readme: ./../README.md

README.md

 
 ### Documentation
 
-* [Quick Start][quick_start]
-* [Data Format and Document Model][data_and_document]
-* [Style attributes][attributes]
-* [Heuristic rules][heuristics]
-* [Images][images]
-* [FAQ][faq]
-
-[quick_start]: /doc/quick_start.md
-[data_and_document]: /doc/data_and_document.md
-[attributes]: /doc/attributes.md
-[heuristics]: /doc/heuristics.md
-[images]: /doc/images.md
-[faq]: /doc/faq.md
+* [Quick Start](doc/quick-start.md)
+* [Data Format and Document Model](doc/data-and-document.md)
+* [Style attributes](doc/attributes.md)
+* [Heuristic rules](doc/heuristics.md)
+* [Images](doc/images.md)
+* [FAQ](doc/faq.md)
 
 ## Clean and modern look
 
 conflict-free resolution of changes.
 
 > Zefyr editor uses Quill.js **Delta** as underlying data format. Read
-> more about Zefyr and Deltas in our [documentation][data_and_document].
+> more about Zefyr and Deltas in our [documentation](doc/data-and-document.md).
 > Make sure to checkout [official documentation][delta] for Delta format
 > as well.
 

SUMMARY.md

+# Summary
+
+## [About](README.md)
+
+## [Quick Start](doc/quick-start.md)
+
+## Concepts
+
+* [Data Format and Document Model](doc/data-and-document.md)
+* [Attributes](doc/attributes.md)
+* [Heuristic rules](doc/heuristics.md)
+
+## [FAQ](doc/faq.md)

doc/concepts/attributes.md

 ## Style Attributes
 
 > If you haven't yet, read introduction to Zefyr document model called
-> Notus [here][data_and_document];
+> Notus [here](data-and-document.md);
 
 Style attributes in Notus documents are simple key-value pairs, where
 keys identify the attribute and value describes the style applied, for
 The `block` attribute in Notus documents is line-scoped. To change a
 group of lines from "bullet list" to "number list" we need to update
 block style on each of the lines individually. Zefyr editor abstracts
-away such details with help of [heuristic rules][heuristics].
+away such details with help of [heuristic rules](heuristics.md).