Document metrics store SSL settings.

docs/configuration.rst

@@ -124,7 +124,7 @@ Rally will ask you a few more things in the advanced setup:
 * **Elasticsearch project directory**: This is the directory where the Elasticsearch sources are located. If you don't actively develop on Elasticsearch you can just leave the default but if you want to benchmark local changes you should point Rally to your project directory. Note that Rally will run builds with Gradle in this directory (it runs ``gradle clean`` and ``gradle :distribution:tar:assemble``).
 * **JDK root directory**: Rally will only ask this if it could not autodetect the JDK home by itself. Just enter the root directory of the JDK you want to use. By default, Rally will choose Java 8 if available and fallback to Java 9.
 * **Metrics store type**: You can choose between ``in-memory`` which requires no additional setup or ``elasticsearch`` which requires that you start a dedicated Elasticsearch instance to store metrics but gives you much more flexibility to analyse results.
-* **Metrics store settings** (only for metrics store type ``elasticsearch``): Provide the connection details to the Elasticsearch metrics store. This should be an instance that you use just for Rally but it can be a rather small one. A single node cluster with default setting should do it.
+* **Metrics store settings** (only for metrics store type ``elasticsearch``): Provide the connection details to the Elasticsearch metrics store. This should be an instance that you use just for Rally but it can be a rather small one. A single node cluster with default setting should do it. When using self-signed certificates on the Elasticsearch metrics store, certificate verification can be turned off by setting the ``datastore.ssl.verification_mode`` setting to ``none``. Alternatively you can enter the path to the certificate authority's signing certificate in ``datastore.ssl.certificate_authorities``. Both settings are optional.
 * **Name for this benchmark environment** (only for metrics store type ``elasticsearch``): You can use the same metrics store for multiple environments (e.g. local, continuous integration etc.) so you can separate metrics from different environments by choosing a different name.
 * whether or not Rally should keep the Elasticsearch benchmark candidate installation including all data by default. This will use lots of disk space so you should wipe ``~/.rally/benchmarks/races`` regularly.