Remove unnecessary whitespace from code blocks in READMEs

[ryotaro-shirai]

Motivation / Background

• This PR removes unnecessary leading whitespaces from code blocks in README.md and lib/locales/README.md.
• Since other code blocks do not have these whitespaces, removing them ensures consistency and improves overall readability.
• I have verified that no other instances exist by running the following command:
  grep -RIn --include='*.md' ' Faker' .

Affected lines:

./README.md:160:   Faker::Config.random = Random.new
./lib/locales/README.md:55:   Faker::Config.locale = :es
./CHANGELOG.md:2788:-  Faker::Vehicle.vin gives undefined method `match' [\#638](https://github.com/stympy/faker/issues/638)
./CONTRIBUTING.md:134:#   Faker::Alphanumeric.alpha #=> "kgdpxlgwjirlqhwhrebvuomdcjjpeqlq"
./CONTRIBUTING.md:135:#   Faker::Alphanumeric.alpha(number: 10) #=> "zlvubkrwga"

Note: This excludes CHANGELOG.md and CONTRIBUTING.md.

Additional information

Checklist

Before submitting the PR make sure the following are checked:

• This Pull Request is related to one change. Changes that are unrelated should be opened in separate PRs.
• Commit message has a detailed description of what changed and why. If this PR fixes a related issue include it in the commit message. Ex: [Fix #issue-number]
• Tests are added or updated if you fix a bug, refactor something, or add a feature.
• Tests and Rubocop are passing before submitting your proposed changes.

If you're proposing a new generator or locale:

• Double-check the existing generators documentation to make sure the new generator you want to add doesn't already exist.
• You've reviewed and followed the Contributing guidelines.