chore: Adds npm script to fix README instructions (fix #904)

[dvargas92495]

Please check if the PR fulfills these requirements

• It's the right issue type on the title
• When resolving a specific issue, it's referenced in the PR's title (e.g. fix #xxx[,#xxx], where "xxx" is the issue number)
• The commit message follows our guidelines
• Tests for the changes have been added (for bug fixes/features)
• Docs have been added/updated (for bug fixes/features)
• It does not introduce a breaking change or has a description of the breaking change

Description

I was working on #1188 when I ran into the README being out of date. Took this as an opportunity to update them with a script that does all the steps outlined here, which unblocked me during local development

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Thank you for your contribution to TOAST UI product. 🎉 😘 ✨

[seonim-ryu]

I reviewed it and it's nice that the way you added will be improved to make it easier to develop. This PR will be merged. Thanks for the contribution. 👍