Provide some default output when tool is signing

**Is your feature request related to a problem? Please describe.**
It was not clear to me that the tool was working due to other issues in my CI, see background in https://github.com/dotnet-foundation/wg-maintainers/issues/90#issuecomment-1684531111. This caused me to spend a lot of time poking the `sign` tool than finding my ultimate problem in my build configuration.

It wasn't until I did `--verbosity Debug` that I saw it actively doing things, but that was hard to find out to even turn on as an option as that PR is still open #541.

**Describe the solution you'd like**
It'd be nice at minimum for the tool to spit out something like

13 Packages Signed

to the console, or maybe even better like:

Signed CommunityToolkit.Uwp.Animations.nupkg
Signed CommunityToolkit.Uwp.Behaviors.nupkg
...
13 Packages Signed

Then maybe there should be an additional `-s|--silent` parameter which suppresses this default output if it's unwanted.

**Describe alternatives you've considered**
🤷‍♂️ don't know how else this would have gone differently since the tool doesn't give me any information outside a success code. Since it's meant to run in a CI, it's not something you generally try and test and poke locally.

It would have been nice to have more docs on the CLI parameters discoverable from the readme of the repo though, hopefully #541 on that side can be merged soon.

**Additional context**
Version: `0.9.1-beta.23356.1`
Background: https://github.com/dotnet-foundation/wg-maintainers/issues/90#issuecomment-1684531111