added series aggregation to README

Author: oberschlauberger

README.md

@@ -36,7 +36,7 @@ To construct a metric query, first create a new panel on a dashboard and select
 ### Query Builder
 When you add a new query for a panel, the query builder mode is used by default. Simply click the respective buttons to browse and select agent, metric, and data frequency for your query.
 ### Raw Query Mode
-Click "Toggle Edit Mode" on the right-hand triple bar menu to switch to raw query mode. Although the query builder mode supports basic regular expressions, you can use the raw query mode to use more advanced regex features. Some regular expressions might require that you disable automatic escaping by toggling the respective checkbox.
+Click "Toggle Edit Mode" on the right-hand triple bar menu to switch to raw query mode. Although the query builder mode supports basic regular expressions, you can use the raw query mode to use more advanced regex features. Some regular expressions might require that you disable automatic escaping by toggling the respective checkbox. Additionally, raw query mode supports the aggregation of multiple series into a single aggregated series for display.
 
 ### Query Variables
 You can create variables for templating based on APM queries. You can either query for agents or metrics. For agents, prepend your agent regex with "Agents|", for metrics use "Metrics|" instead. For example, "Agents|.+" will get you all agents. Use the regex option to transform your query results. See the animation below for an example of an agent query:
@@ -45,6 +45,11 @@ You can create variables for templating based on APM queries. You can either que
 ### Temporal Resolution Variable
 Considering the different temporal aggregation levels of CA APM, it makes sense to use a template variable to control the temporal resolution of time series data dynamically. Simply create a custom dashboard variable and use `15s,30s,1m,2m,6m,12m,24m,48m,1h,168m,12h` for the values.
 
+### Series Aggregation
+In raw query mode, you can choose an aggregation mode to aggregate multiple metrics into a single series of values. This way, you can get a single aggregated time series for visualization in Grafana if your query returns multiple metrics. The implemented aggregation modes are _sum_, _mean_, _max_, _min_, and _median_. Be careful when your metrics might contain null values - these are not explicitly handled by the aggregation methods.
+
+![Series-Aggregation](https://github.com/NovaTecConsulting/ca-apm-grafana-datasource/blob/master/media/series_aggregation.jpg)
+
 ## License
 
 Copyright (c) 2017 Novatec Consulting GmbH. All rights reserved.