[Feature Request] Placeholder question in search bar

[salma-emara]

Is your feature request related to a problem? Please describe.
The placeholder question in semantic search is "what is a pointer" and "pointer" in keyword search. It confuses me, as when I search, and then look again at the search bar, I find a question I didn't ask.

Describe the solution you'd like
Maybe have "Semantically search book ..." and "Keyword search book ..." respectively.

Describe alternatives you've considered (Optional)
Ideally, in the search.html page, the search bar should store the last question that was searched, but it's okay if we reset the contents of the bar to the default placeholder.