docs: add Trivy scan badges

| Input / Variable | Description                              | Default value     |

| --------------------- | ---------------------------------------- | ----------------- |

| `image` / `PUPPETEER_IMAGE` | The Docker image used to run Puppeteer   | `ghcr.io/puppeteer/puppeteer:latest` |

| `image` / `PUPPETEER_IMAGE` | The Docker image used to run Puppeteer   | `ghcr.io/puppeteer/puppeteer:latest` <br/>[![Trivy Badge](https://to-be-continuous.gitlab.io/doc/secu/trivy-badge-PUPPETEER_IMAGE.svg)](https://to-be-continuous.gitlab.io/doc/secu/trivy-PUPPETEER_IMAGE) |

| `project-dir` / `PUPPETEER_PROJECT_DIR` | The Puppeteer project directory (containing `package.json`) | `.` |

| `test-extra-args` / `PUPPETEER_TEST_EXTRA_ARGS` | Testing framework extra options based on [Jest](https://jestjs.io/docs/en/cli) | _none_ |

| `review-enabled` / `REVIEW_ENABLED` | Set to `true` to enable Puppeteer tests on review environments (dynamic environments instantiated on development branches) | _none_ (disabled) |