docs: code highlighting configuration

[decentral1se]

Description

From https://squidfunk.github.io/mkdocs-material/reference/code-blocks/

Before:

After:

Checklist

• I/we have read the GoToSocial contribution guidelines.

[tsmethurst]

Thanks! Does this necessitate any new dependencies? Or does it just use the existing things in docs/environment.yml?

[decentral1se]

@tsmethurst no new deps! cool, didn't see docs/environment.yml but that's exactly what i installed to get things up and running. so, yeh, i think this is just out-of-the-box functionality from mkdocs-material.

[daenney]

mkdocs-material declares a dependency on pygments and pymdown-extensions so we're good to go here. No other tweaking aside from the config options is necessary.

[tsmethurst]

Nice one, thank you! :)