Add tooltips for sub-category folder

[pujiaxun]

Background: I wonder how many problems I have solved. Then I found the tooltip field is available for now. That's it~

[jdneo]

@pujiaxun Sounds great. Would you mind to attach a screenshot in the PR?

[pujiaxun]

@pujiaxun Sounds great. Would you mind to attach a screenshot in the PR?

It looks like this. @jdneo

[jdneo]

@pujiaxun Just one small comment.

[pujiaxun]

        import * as os from "os";
        //...

        return [
            `AC: ${numAC}`,
            `Not AC: ${numNotAC}`,
            `Unknown: ${numUnknown}`,
            `Total: ${problems.length}`,
        ].join(os.EOL);

Like this? @jdneo

[jdneo]

@pujiaxun Yes, looks much better.

[pujiaxun]

@jdneo Any other suggestions? For instance, I think the name "Not AC" sounds weird...

[jdneo]

@pujiaxun hmm, good question.

Regarding the wording. My suggestion is Not AC -> Failed

Either Unknown or Total, one of them can be removed I think? What do you think?

[pujiaxun]

@jdneo I prefer to keep Total if I have to give up one of them. After all, the tag Unknown is somewhat confusing.

[jdneo]

Same to me. So let's keep AC, Failed and Total.

[jdneo]

Just one more comment

[jdneo]

@pujiaxun LGTM. Thank you for your contribution. Nice work.