Improve code block rendering with larger indentation

[jibidus]

code block with tab indentation has a better output :

With 1 tab :

With 2 spaces :

• Step 1 : document this
• Step 2 : make space indentation work (if possible)

[jibidus]

We could complete documentation to explain how to customize code block with this link: https://gohugo.io/content-management/syntax-highlighting/#highlight-shortcode

[jibidus]

Spaces and tabs indentation work well (with jetBrains Mono font). 4 spaces = 1 tab.
1 item added in documentation about that + #219 to encourage 4 spaces (not 2)