docs: change i.e. to e.g. in search placeholder

[pwbriggs]

What's the problem this PR addresses?

In the website search placeholder text (something like Search packages (i.e. babel, webpack, react, ...)), the word "i.e." is used incorrectly. "i.e." means "that is," but the intended meaning here is "e.g.," meaning "for example."

How did you fix it?

Changed the three instances I found of this placeholder text to use "e.g." instead.

Checklist

• I have read the Contributing Guide.

• I have set the packages that need to be released for my changes to be effective.
  👆 Not sure how to do that / if it's applicable to docs-only changes. never mind, see comment below.

• I will check that all automated PR checks pass before the PR gets reviewed.

[pwbriggs]

Sorry, I just realized that I changed a search placeholder that wasn't on the website. I undid that change, so now the tests should pass. (We should also update that placeholder in plugin-interactive-tools, but I think that belongs in another PR.)