Readme: Clarify filename of prettierrc

[tordans]

The Readme uses a specific way to specify the prettierrc configs but does not explicitly state which file name is used.

Prettier supports all kinds of formats (https://prettier.io/docs/en/configuration.html). I had to lookup that this is likely the format referenced here.

By making this more explicit it makes it easier to use the given example.

[changeset-bot]

⚠️ No Changeset found

Latest commit: e9e9884

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types

Click here to learn what changesets are, and how to add one.

Click here if you're a maintainer who wants to add a changeset to this PR

[Princesseuh]

Thank you, this is great!