docs: add diagrams link to README.md

[alexkarezin]

Summary:

Adding a link to the high-level diagrams including module, library dependency and others (https://sourcespy.com/github/mobilitydatagtfsvalidator/). Built directly from source and updated on schedule. Intended to simplify developer's introduction to the project.

In the spirit of transparency - I am the author of the diagrams. Hope contributors find it useful.

Expected behavior:

No behavior changes

• [x] Run the unit tests with gradle test to make sure you didn't break anything
• [x] Format the title like "feat: [new feature short description]". Title must follow the Conventional Commit Specification(https://www.conventionalcommits.org/en/v1.0.0/).
• [x] Linked all relevant issues
• [x] Include screenshot(s): link

[welcome[bot]]

Thanks for opening this pull request! You're awesome. We use semantic commit messages to streamline the release process. Before your pull request can be merged, you should update your pull request title to start with a semantic prefix. Examples of titles with semantic prefixes:

• fix: Bug with ssl network connections + Java module permissions.
• feat: Initial support for multiple @PrimaryKey annotations.
• docs: update RELEASE.md with new process To get this PR to the finish line, please do the following:
• Read our Contribution Guidelines
• Follow Google Java style coding standards
• Include tests when adding/changing behavior
• Include screenshots

[CLAassistant]

All committers have signed the CLA.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[alexkarezin]

David, I feel a little bit lost here... I don't believe I caused the said job failure. Can the job be restarted? A little help please. Thanks!!!