warp-cli, warp-diag: add page

[reinhart1010]

• The page (if new), does not already exist in the repository.
• The page is in the correct platform directory (common/, linux/, etc.)
• The page has 8 or fewer examples.
• The PR title conforms to the recommended templates.
• The page follows the content guidelines.
• The page description includes a link to documentation or a homepage (if applicable).

Version of the command being documented (if known): WARP 2021.8.1

As far as I know the CLI client for WARP is only available on Linux. That's why I put it inside linux/ instead of common/.

[reinhart1010]

Oh wait I forgot warp-diag

[marchersimon]

Thanks @reinhart1010

[reinhart1010]

Tested in macOS and it seems that warp-cli works as well.

But I notice that warp-cli is not available on Windows after first install, maybe that's because I haven't rebooted and update the $PATH?