docs(contributing): add introduction to contributing and update flowchart to include major and minor contributions

[evzzk]

Issue # (if applicable)

Closes #.

Reason for this change

Make it easier for those new to contributing and for those submitting small contributions to get started.

Description of changes

Provide introductory information on what a contribution is. Add a new definition of major and minor contributions. The purpose of these new terms are to distinguish between two different types of contributions for two reasons: (1) Provide a clearer and simpler path to contributing for those submitting small changes like doc improvements or bug fixes; and (2) Provide a separate path of submitting an RFC to discuss implementation details before someone puts in the time and effort of submitting a major contribution.

I also updated the flowchart to highlight these two paths and show how they differ.

Next steps after this revision are to improve the "getting started" documentation and restructure content based on the updated flowchart.

Describe any new or updated permissions being added

<!— What new or updated IAM permissions are needed to support the changes being introduced ? -->

Description of how you validated changes

Checklist

• My code adheres to the CONTRIBUTING GUIDE and DESIGN GUIDELINES

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By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.39%. Comparing base (72e089b) to head (33c26fa).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #32619   +/-   ##
=======================================
  Coverage   81.39%   81.39%           
=======================================
  Files         225      225           
  Lines       13714    13714           
  Branches     2411     2411           
=======================================
  Hits        11162    11162           
  Misses       2277     2277           
  Partials      275      275           

Flag	Coverage Δ
suite.unit	81.39% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
packages/aws-cdk	80.70% <ø> (ø)
packages/aws-cdk-lib/core	82.10% <ø> (ø)

[mergify]

Thank you for contributing! Your pull request will be updated from main and then merged automatically (do not update manually, and be sure to allow changes to be pushed to your fork).

[mergify]

Thank you for contributing! Your pull request will be updated from main and then merged automatically (do not update manually, and be sure to allow changes to be pushed to your fork).

Pull request has been modified.

[mergify]

Thank you for contributing! Your pull request will be updated from main and then merged automatically (do not update manually, and be sure to allow changes to be pushed to your fork).

[aws-cdk-automation]

AWS CodeBuild CI Report

• CodeBuild project: AutoBuildv2Project1C6BFA3F-wQm2hXv2jqQv
• Commit ID: 33c26fa
• Result: SUCCEEDED
• Build Logs (available for 30 days)

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[mergify]

Thank you for contributing! Your pull request will be updated from main and then merged automatically (do not update manually, and be sure to allow changes to be pushed to your fork).

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