Add quickstart to README

[mfisher87]

Currently, the README doesn't give a feel for what earthaccess does. This helps the user envision how they would use it right way. The README should act as the top of the funnel into our docs. It's wide and shallow and guides people to the depth they are looking for.

Pull Request (PR) draft checklist - click to expand

• Please review our
  contributing documentation
  before getting started.
• Ensure an issue exists representing the problem being solved in this PR.
• Populate a descriptive title. For example, instead of "Updated README.md", use a
  title such as "Add testing details to the contributor section of the README".
• Populate the body of the pull request with:
  • A clear description of the change you are proposing.
  • Links to any issues resolved by this PR with text in the PR description, for
    example closes #1. See
    GitHub docs - Linking a pull request to an issue.
• Update CHANGELOG.md with details about your change in a section titled
  ## Unreleased. If such a section does not exist, please create one. Follow
  Common Changelog for your additions.
• Update the documentation and/or the README.md with details of changes to the
  earthaccess interface, if any. Consider new environment variables, function names,
  decorators, etc.

Click the "Ready for review" button at the bottom of the "Conversation" tab in GitHub
once these requirements are fulfilled. Don't worry if you see any test failures in
GitHub at this point!

Pull Request (PR) merge checklist - click to expand

Please do your best to complete these requirements! If you need help with any of these
requirements, you can ping the @nsidc/earthaccess-support team in a comment and we
will help you out!

• Add unit tests for any new features.
• Apply formatting and linting autofixes. You can add a GitHub comment in this Pull
  Request containing "pre-commit.ci autofix" to automate this.
• Ensure all automated PR checks (seen at the bottom of the "conversation" tab) pass.
• Get at least one approving review.

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📚 Documentation preview 📚: https://earthaccess--789.org.readthedocs.build/en/789/

[mfisher87]

We need to migrate to Ruff 0.6.0 to get these linting errors to quiet down.

[asteiker]

This is a good, basic example to include here!