docs: Update README.md

[targeral]

Fix parameter error in pnpm add command

What's added in this PR?

Provide an implementation summary. What did you add beyond the described task? What are the additional details you'd like people to pay attention to? To help people review this PR understand what's changed.

Replace pnpm add --dev to pnpm add --save-dev.

Screenshots

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What's the issues or discussion related to this PR ?

Provide some background information related to this PR, including issues or task. Prior to this PR what's the behavior that wasn't expected.

If there wasn't discussion related to this PR, you can include the reasoning behind this PR of why you did it.

What are the steps to test this PR?

To help reviewer and tester to understand what's needed

Documentation update for this PR (if applicable)?

Add documentation if how the application will behave differently than previous state. Copy paste your PR in zephyr-documentation PR link here.

(Optional) What's left to be done for this PR?

(Optional) What's the potential risk and how to mitigate it?

(Required) Pre-PR/Merge checklist

• I have added/updated/opened a PR to documentation to cover this new behavior
• I have added an explanation of my changes
• I have written new tests (if applicable)
• I have tested this locally (standing from a first time user point of view, never touch this app before)
• I have/will run tests, or ask for help to add test

[cla-assistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution.
1 out of 2 committers have signed the CLA.

✅ arthurfiorette
❌ targeral
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[cla-assistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[Nsttt]

Please sign the CLA @targeral :)