clarify node.js tracer docs for esbuild RE init

[tlhunter]

What does this PR do? What is the motivation?

• clarify init requirements when bundling a node app

Merge instructions

Merge readiness:

• [x] Ready for merge

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Additional notes

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Preview links (active after the build_preview check completes)

Modified Files

• https://docs-staging.datadoghq.com/tlhunter/node-esbuild-clarify/tracing/trace_collection/automatic_instrumentation/dd_libraries/nodejs