Document remaining v1.0.0 breaking changes in README - #474

CodeQL Action major versions v1 and v2 have been deprecated. Please update all occurrences of the CodeQL Action in your workflow files to v3. For more information, see https://github.blog/changelog/2025-01-10-code-scanning-codeql-action-v2-is-now-deprecated/

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v3, github/codeql-action/analyze@v2, github/codeql-action/autobuild@v2, github/codeql-action/init@v2. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/