Fix link to instrumentation

The current link points to 404. Following this open-telemetry#1797, the docs for instrumentation were moved to contrib

docs/index.rst

@@ -34,7 +34,7 @@ In addition, there are several extension packages which can be installed separat
     pip install opentelemetry-instrumentation-{instrumentation}
 
 These are for exporter and instrumentation packages respectively.
-Some packages can be found in :scm_web:`instrumentation <instrumentation/>` and :scm_web:`exporter <exporter/>`
+Some packages can be found in `instrumentation <https://github.com/open-telemetry/opentelemetry-python-contrib/tree/main/instrumentation>`_ and :scm_web:`exporter <exporter/>`
 directory of the repository. The remaining packages can be found at the 
 `Contrib repo instrumentation <https://github.com/open-telemetry/opentelemetry-python-contrib/tree/main/instrumentation>`_
 and `Contrib repo exporter <https://github.com/open-telemetry/opentelemetry-python-contrib/tree/main/exporter>`_ directories.