Add usage example to module documentation

[spencerarq]

Description

This PR adds a basic usage example to the K6 module documentation, as requested in issue #8780.

Currently, the documentation lacks a clear starting point for instantiating the container. This example provides a simple, copy-pasteable block to improve the Developer Experience (DX) for new users.

Changes

• Added a Usage section to docs/modules/k6.md with a standard try-with-resources example.

Related Issue

Fixes #8780