docs: fix link to Prometheus Instrumentation example (#4769)

Author: felixhummel

docs/examples/metrics/prometheus-grafana/README.rst

@@ -3,7 +3,7 @@ Prometheus Instrumentation
 
 This shows how to use ``opentelemetry-exporter-prometheus`` to automatically generate Prometheus metrics.
 
-The source files of these examples are available :scm_web:`here <docs/examples/prometheus-grafana/>`.
+The source files of these examples are available :scm_web:`here <docs/examples/metrics/prometheus-grafana/>`.
 
 Preparation
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