Didn't help - revert.

book/src/SUMMARY.md

@@ -1,6 +1,7 @@
 # Summary
 
-- [Introduction](./chapter_0.md)
+[Introduction](./chapter_0.md)
+
 - [Section 1 - Hello Rust](./chapter_1.md)
     - [Hello Rust](./chapter_1.md)
     - [Entities & Components](./chapter_2.md)