[FEATURE] Add Device Count in detect cli command

[webbcam]

Ideal Solution

e.g.
tiflash detect

Additional context
Add any other context or screenshots about the feature request here.

Feature Description
The 'detect' command should print out the number of devices found when run on the command line.

Why feature is requested
When a computer has a large amount of devices connected to, it's a pain for the user to manually count the number of devices detected by tiflash. Having this extra print out in the end is useful for the user.

Describe the solution you'd like
At the end of the print out from running tiflash detect on command line, a total count of devices found would be printed out.

e.g. printing out "Found 5 devices." or "5 devices found."