update kramdown

Author: aott33

_config.yml

@@ -70,9 +70,16 @@ mermaid: true
 
 # Site-wide kramdown syntax highlighting
 kramdown:
+  footnote_backlink: "↩︎"
   syntax_highlighter: rouge
-  syntax_highlighter_opts:
-    css_class: 'highlight'
+  syntax_highlighter_opts: # Rouge Options › https://github.com/jneen/rouge#full-options
+    css_class: highlight
+    # default_lang: console
+    span:
+      line_numbers: false
+    block:
+      line_numbers: true
+      start_line: 1
 
 # Collections configuration
 collections: