[Feature request] Showing a loading message when PRs / Issues are being fetched

[kyu08]

Is your feature request related to a problem? Please describe.

I felt strange slightly about that a message No PRs were found that match the given filters is showed when I launch gh-dash.

The message might not friendly for users.

Describe the solution you'd like

Showing loading message like Loading... like this:

Describe alternatives you've considered

N/A

Additional context

N/A