Update Japanese README

[rlinehan]

We've recently made a number of updates to the English README due to changes in CLI commands (removal of momento account signup). We need to update the Japanese README to match.

[codemountains]

@rlinehan @poppoerika

Hi,

I've submitted a pull request (#333) to address this issue. This is my first contribution to momento-cli, so I would greatly appreciate any feedback or suggestions for improvement.

Thank you for considering my contribution.