Add browser-based workflow runner guide for n8n deployments

[Copilot]

The issue asks for a web-based way to add, modify, and run n8n workflows. This PR adds focused documentation that turns the deployed n8n UI into a clear “workflow runner” path for day-to-day workflow authoring and execution.

• What was added

  • New guide: docs/WORKFLOW-RUNNER.md
  • Documents the core UI flows:
    • create a workflow
    • edit existing workflows
    • execute manually
    • activate trigger-based execution
    • import/export workflow JSON

• Where it was integrated

  • Linked from README.md under Getting Started for discoverability.
  • Linked from docs/SIMPLE-MODE.md so users landing in the default deployment path can immediately manage workflows in-browser.

• Representative snippet

  ### Getting Started
  - **[Deployment Guide](DEPLOY_TO_DO.md)** - Step-by-step deployment
  - **[Environment Variables](ENV_TEMPLATE.md)** - Configuration reference
  - **[Workflow Web Runner](docs/WORKFLOW-RUNNER.md)** - Add, modify, and run workflows in the n8n UI

Original prompt

n8n workflows webpage runner that i can add/ modify/ run any n8n workflow.