[DO-601] Features page - links updated (#56)

Author: StanG4313

docs/content/2.features/1.index.md

@@ -11,4 +11,5 @@ Contents:
 
 1. [Notice](/features/notice)
 2. [Term](/features/term)
-3. [Diagram](/features/mermaid)
+3. [Mermaid.js](/features/mermaid)
+4. [SEO](/features/seo)