feat: add workflow to test readme generation

[virajbhartiya]

Description

Created a workflow to search for README.docify.md in the repo, and run cargo build --features generate-readme in the dir of the file (assuming it is related to a crate). If the git diff shows some output for the README.md, then the file update wasn't pushed on the branch, and the workflow fails.
Closes #6331

Integration

Downstream projects that want to adopt this README checking workflow should:

1. Copy the .github/workflows/readme-check.yml file to their repository
2. Ensure any README.docify.md files in their project follow the expected format
3. Implement the generate-readme feature flag in their Cargo.toml if not already present

Review Notes

This PR adds a GitHub Actions workflow that automatically verifies README.md files are up-to-date with their corresponding README.docify.md sources. Key implementation details:

• The workflow runs on both PRs and pushes to main
• It finds all README.docify.md files recursively in the repository
• For each file found:
  • Builds the project with --features generate-readme in that directory
  • Checks if the README.md has any uncommitted changes
  • Fails if any README.md is out of sync

[cla-bot-2021]

User @virajbhartiya, please sign the CLA here.