Document the default SDK instrumentation requires elevated permissions

[MrAlias]

The autosdk probe use bpf_probe_write_user to enable the auto/sdk package but also to write trace/span IDs:

opentelemetry-go-instrumentation/internal/pkg/instrumentation/bpf/go.opentelemetry.io/auto/sdk/bpf/probe.bpf.c

Lines 55 to 74 in 787af33

	void *tid = (void *)(go_sc + span_context_trace_id_pos);
	long ret = bpf_probe_write_user(tid, &sc->TraceID, TRACE_ID_SIZE);
	if (ret != 0) {
	bpf_printk("write_span_context: failed to write trace ID: %ld", ret);
	return -2;
	}
	void *sid = (void *)(go_sc + span_context_span_id_pos);
	ret = bpf_probe_write_user(sid, &sc->SpanID, SPAN_ID_SIZE);
	if (ret != 0) {
	bpf_printk("write_span_context: failed to write span ID: %ld", ret);
	return -3;
	}
	void *flags = (void *)(go_sc + span_context_trace_flags_pos);
	ret = bpf_probe_write_user(flags, &sc->TraceFlags, TRACE_FLAGS_SIZE);
	if (ret != 0) {
	bpf_printk("write_span_context: failed to write trace flags: %ld", ret);
	return -4;
	}

This is required to correctly support trace context propagation and integration with the auto-instrumentation telemetry.

Because of this fundamental requirement, there are no known replacements for using this BPF API. Meaning that a non-locked down kernel and elevated permissions are required to run this probe. This needs to be clearly documented and the alternate behavior when this is not supported needs to be explained to users.