fix: use spaces for readme b/c npmjs.org does not format tabs well

[tylersayshi]

first: I love create-typescript-app... it was a fantastic way for me to get my project off the ground with good feeling lint defaults and not having to think much about it 🙌

this is only a recommendation and the more correct fix would be better default tab spaces view on npmjs.com, but that sounds unlikely?

here's an example of when it's bad
https://www.npmjs.com/package/prototypey/v/0.2.3
vs with spaces
https://www.npmjs.com/package/prototypey/v/0.2.4

PR Checklist

• Addresses an existing open issue: fixes 🛠 Tooling: suggestion to use spaces only for readme.md b/c of npmjs.com #2277
• That issue was marked as status: accepting prs
• Steps in CONTRIBUTING.md were taken

Overview

This is a recommendation as a default so others don't go through the same pain with npm after publishing, but please feel free to just close if this is out of scope for the project or anything.

[github-actions]

👋 Hi @tylersayshi, thanks for the pull request! A scan flagged a concern with it. Could you please take a look?

[pr-task-completion] This PR's body is missing [x] checks on the following tasks from the PR template.

• That issue was marked as status: accepting prs

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[tylersayshi]

I realize this issue is not yet marked accepting PRs but had already made the minor changes, so figured i'd leave them 😅

[JoshuaKGoldberg]

I appreciate you so much for sending this!! Switching to draft pending discussion in #2277 but at the very least it's great as a reference. Thank you!