add option to add extra comments to the pull request description for update command

[anatawa12]

Description of the new feature / enhancement

I wonder if wingetcreate.exe update option to add extra comments to the pull request description for update command.

In my workflow, pull request targeting other repository is created by my machine account (@anatawa12-bot) but I should watch the pull request so I want to mention me on the pull request.
however, wingetcreate command doesn't have any way to know pull request number programmatically so I want some option to append some custom string to the pull request message.

Proposed technical implementation details

appending text from command line option here.

winget-create/src/WingetCreateCore/Common/GitHub.cs

Line 370 in c804449

string description = await this.GetFileContentsAsync(PRDescriptionRepoPath);