Specify syntax highlighting for shell output

For the sake of consistency and simplicity, we're specifying to use
'shell' instead of 'bash' or 'sh' for most syntax highlighting most
shell output. The exception: code blocks that contain `sudo`,
because Mike Jang discovered it causes oddities in the syntax
highlighting output. For code blocks containing `sudo`, we're now
specifying to use `console` instead.`

doc/development/documentation/styleguide.md

@@ -795,7 +795,8 @@ nicely on different mobile devices.
 - To display raw Markdown instead of rendered Markdown, you can use triple backticks
   with `md`, like the `Markdown code` example above, unless you want to include triple
   backticks in the code block as well. In that case, use triple tildes (`~~~`) instead.
-- [Syntax highlighting for code blocks](https://github.com/rouge-ruby/rouge/wiki/List-of-supported-languages-and-lexers) is available for many languages.
+- [Syntax highlighting for code blocks](https://github.com/rouge-ruby/rouge/wiki/List-of-supported-languages-and-lexers)
+  is available for many languages. Use `shell` instead of `bash` or `sh` for shell output.
 - For a complete reference on code blocks, check the [Kramdown guide](https://about.gitlab.com/handbook/product/technical-writing/markdown-guide/#code-blocks).
 
 ## GitLab SVG icons