Add QNX Everywhere setup instructions to repository documentation

[4og]

What

The documentation in this repository is missing information on how to obtain a QNX Everywhere license and how to configure it locally so that modules using bazel_cpp_toolchains can use it correctly.

It would be helpful to provide documentation similar to the https://github.com/eclipse-score/toolchains_qnx/blob/main/README.md#where-to-obtain-the-qnx-80-sdp

However, instead of referring users to external videos, a step-by-step guide directly in the repository documentation would make the setup process easier to follow and more accessible. This guide could cover:

• How to obtain a QNX Everywhere license
• How to install and activate the license
• Required environment variables and local configuration
• How to verify that bazel_cpp_toolchains can successfully use the QNX installation

Acceptance Criteria (DoD)

• There is a guide to set up the personal QNX environment

[nradakovic]

I agree that we should document the QNX environment setup required by this module, but I would avoid duplicating QNX’s official licensing and installation documentation in full.

The repository should document the integration contract for bazel_cpp_toolchains, namely:

• where users should obtain the QNX SDP/license from, with links to official QNX resources
• which local installation layout this module expects
• which environment variables or user .bazelrc entries are required, for example QNXLM_LICENSE_FILE
• any Bazel-specific requirements such as sandbox writable paths
• a minimal verification command showing that the QNX toolchain is usable from Bazel

This keeps our documentation maintainable and avoids becoming a stale copy of vendor documentation, while still giving users a complete path for making this Bazel module work locally.