docs: hide system-specific TOC

[joscha]

Hide TOC for installing the CLI

Description:

Not all options are valid for all systems. Brew installs auto completions automatically for example and the order is different, which makes the links go nowhere unless you are in the powershell tab.

Is this change user facing?

NO

References (if applicable):

[mieubrisse]

Thanks for this @joscha ! There's actually a fix that doesn't require disabling completely (basically increasing the floor threshold of header level to be displayed in the sidebar) that'll go in in #2222 . Thanks for highlighting this!