Expand `definition` section of NXData by default

[loichuder]

At https://manual.nexusformat.org/classes/base_classes/NXdata.html, there are a lot of interesting examples in the Description field.

Unfortunately, this section is collapsed when you land on the page and unless you notice a tiny little arrow, you miss a lot of cool stuff.

Could it possible to have the description section visible by default when landing on https://manual.nexusformat.org/classes/base_classes/NXdata.html?