Add ⚡️ content to `Private key management` > Section landing page

[GBKS]

[danielnordh]

Having looked at this page I don't think it needs to change.
The first introduction to Lightning should probably be on the 'Overview' page.

[pavlenex]

I agree, doesn't look we need to add anything here. The only updates that could be done are after page re-ordering in #550

I think we can close this one.

[Bosch-0]

Yep agree this doesn't require any additions.