nodejs doc: add clarification to node.js getting started

[maryliag]

One common approach to register de API is to set the environment variable NODE_OPTIONS with --require @opentelemetry/auto-instrumentations-node/register, but if we follow the Getting Started for Node.js, the step to use --require ./instrumentation.ts on command line can cause a conflict, resulting on an error message similar to:

Error: @opentelemetry/api: Attempted duplicate registration of API: trace
    at registerGlobal (/Users/maryliag/development/otel/opentelemetry-js/api/src/internal/global-utils.ts:47:17)
    at TraceAPI.setGlobalTracerProvider (/Users/maryliag/development/otel/opentelemetry-js/api/src/api/trace.ts:67:35)
    at NodeTracerProvider.register (/Users/maryliag/development/otel/opentelemetry-js/packages/opentelemetry-sdk-trace-base/src/BasicTracerProvider.ts:153:11)
    at NodeTracerProvider.register (/Users/maryliag/development/otel/opentelemetry-js/packages/opentelemetry-sdk-trace-node/src/NodeTracerProvider.ts:68:11)
    at NodeSDK.start (/Users/maryliag/development/otel/opentelemetry-js/experimental/packages/opentelemetry-sdk-node/src/sdk.ts:355:20)
    at Object.<anonymous> (/Users/maryliag/development/otel/nodejs-test/instrumentation.ts:17:5)
    at Module._compile (node:internal/modules/cjs/loader:1378:14)
    at Module.m._compile (/Users/maryliag/development/otel/nodejs-test/node_modules/ts-node/src/index.ts:1618:23)
    at Module._extensions..js (node:internal/modules/cjs/loader:1437:10)
    at Object.require.extensions.<computed> [as .ts] (/Users/maryliag/development/otel/nodejs-test/node_modules/ts-node/src/index.ts:1621:12)
Error: @opentelemetry/api: Attempted duplicate registration of API: context
    at registerGlobal (/Users/maryliag/development/otel/opentelemetry-js/api/src/internal/global-utils.ts:47:17)
    at ContextAPI.setGlobalContextManager (/Users/maryliag/development/otel/opentelemetry-js/api/src/api/context.ts:53:26)
    at NodeTracerProvider.register (/Users/maryliag/development/otel/opentelemetry-js/packages/opentelemetry-sdk-trace-base/src/BasicTracerProvider.ts:159:15)
    at NodeTracerProvider.register (/Users/maryliag/development/otel/opentelemetry-js/packages/opentelemetry-sdk-trace-node/src/NodeTracerProvider.ts:68:11)
    at NodeSDK.start (/Users/maryliag/development/otel/opentelemetry-js/experimental/packages/opentelemetry-sdk-node/src/sdk.ts:355:20)
    at Object.<anonymous> (/Users/maryliag/development/otel/nodejs-test/instrumentation.ts:17:5)
    at Module._compile (node:internal/modules/cjs/loader:1378:14)
    at Module.m._compile (/Users/maryliag/development/otel/nodejs-test/node_modules/ts-node/src/index.ts:1618:23)
    at Module._extensions..js (node:internal/modules/cjs/loader:1437:10)
    at Object.require.extensions.<computed> [as .ts] (/Users/maryliag/development/otel/nodejs-test/node_modules/ts-node/src/index.ts:1621:12)
Error: @opentelemetry/api: Attempted duplicate registration of API: propagation
    at registerGlobal (/Users/maryliag/development/otel/opentelemetry-js/api/src/internal/global-utils.ts:47:17)
    at PropagationAPI.setGlobalPropagator (/Users/maryliag/development/otel/opentelemetry-js/api/src/api/propagation.ts:67:26)
    at NodeTracerProvider.register (/Users/maryliag/development/otel/opentelemetry-js/packages/opentelemetry-sdk-trace-base/src/BasicTracerProvider.ts:163:19)
    at NodeTracerProvider.register (/Users/maryliag/development/otel/opentelemetry-js/packages/opentelemetry-sdk-trace-node/src/NodeTracerProvider.ts:68:11)
    at NodeSDK.start (/Users/maryliag/development/otel/opentelemetry-js/experimental/packages/opentelemetry-sdk-node/src/sdk.ts:355:20)
    at Object.<anonymous> (/Users/maryliag/development/otel/nodejs-test/instrumentation.ts:17:5)
    at Module._compile (node:internal/modules/cjs/loader:1378:14)
    at Module.m._compile (/Users/maryliag/development/otel/nodejs-test/node_modules/ts-node/src/index.ts:1618:23)
    at Module._extensions..js (node:internal/modules/cjs/loader:1437:10)
    at Object.require.extensions.<computed> [as .ts] (/Users/maryliag/development/otel/nodejs-test/node_modules/ts-node/src/index.ts:1621:12)

It can be hard to identify the problem from the error message. So this commit adds a small warning to make sure the requirements are not conflicting.

Run the instrumented app after the change:

[cartermp]

/fix:format

[github-actions]

You triggered fix:format action run at https://github.com/open-telemetry/opentelemetry.io/actions/runs/8386497992