Avoid invalid admonition syntax

[ansd]

As described in https://docusaurus.io/docs/markdown-features/admonitions#usage-with-prettier

If you use Prettier to format your Markdown files, Prettier might auto-format your code to invalid admonition syntax. To avoid this problem, add empty lines around the starting and ending directives. This is also why the examples we show here all have empty lines around the content.

[michaelklishin]

This syntax without the empty lines is not invalid, Docusaurus' own docs use it.

We don't use empty lines in admonitions in every other guide. I guess we also do not format them with Prettier so it becomes a matter of taste.