Update yarn install command in ReadMe file

[MiniKeb]

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Have we already discuss this change? PLEASE take into consideration
that this is a personal open source project and nobody is paying me to
do this work. It would be amazing if you could FIRST open an issue to
discuss your change and proposed implementation. It is a terrible
feeling to have to reject a change over a disagreement; especially,
when the author has clearly put in a lot of effort.

Have we discussed this change?

• Yes
• No, but it's a lil' bug that I'm going to squash.

Which of the following does this change fall under?

• New enhancement/feature
• Refactor
• Bug fix
• None of previous proposal, it's just documentation

What changed?

The yarn installation command in README file

Why is this change required?

It's not required, but it'll be more consistent with current yarn command