Provide a method to open the GitHub CLI website from `gh`

### Describe the feature or problem you’d like to solve

`gh` provides a wealth of information about the product's commands and other help content such as `gh reference` or `gh help`. There is also information captured on [GitHub CLI website](https://cli.github.com/) including manual outlining `gh` commands.

GitHub CLI users who prefer web experiences or looking for content that is only on the web have to launch a browser and navigate to the website.

What if `gh` has a `--web` option for opening it up instead?

- `gh --web`?
- `gh help --web`?

### Proposed solution

This would be a minor convenience feature, helping users quickly jump between terminal and browser without searching for the GitHub CLI site.

### Additional context

Add any other context like screenshots or mockups are helpful, if applicable.