Added Usage section to README.

README.md

@@ -27,6 +27,35 @@ This plugin has been tested with Kibana versions 4.3, 4.4 and 4.5.
 bin/kibana plugin -i prelert_swimlane_vis -u https://github.com/prelert/kibana-swimlane-vis/archive/v0.1.0.zip
 ```
 
+## Usage
+
+The first step in creating the visualization is to configure the metric that will be displayed.
+Select the Elasticsearch aggregation to be used - count, average, sum, min and max are currently available.
+If using average, sum, min or max, select the numeric field that will be aggregated. From Kibana 4.5, a 
+custom label can also be entered if desired, which will be displayed against the value in tooltips. In our
+example we are plotting maximum response time, with the numeric value stored in the `actual` field of the results:
+
+![image](resources/step1.png)
+
+The next step is to configure the field by which you want the results to be split to form the swimlanes using
+an Elasticsearch terms aggregation. Select the field for the *View by* bucket aggregation, which will typically be 
+one of the *string* type fields in your results. Use the *Size* dropdown to select the maximum number of swimlanes 
+that will be displayed. In our example, we will be viewing results by `airline`, showing the top 15 airlines by
+maximum response time:
+
+![image](resources/step2.png)
+
+Note if no *View by* buckets are configured, a single swimlane will be displayed showing the behavior of the 
+selected metric over all results.
+
+The final step is to select the time field in your results. The time frame for the intervals in the swimlane
+visualization can be specified in terms of seconds, minutes, hours, days, weeks, months, or years, or just 
+leave it to the *Auto* setting of Kibana which will aim to pick the optimum interval depending on the time
+span of the query. An *interval* dropdown control is also available at the top of the swimlane for use when
+the visualization has been saved and added to a dashboard.
+
+![image](resources/step3.png)
+
 ## Options
 
 The options tab allows you to configure the color band thresholds and the format of the value shown
@@ -53,6 +82,8 @@ enter the desired value, noting that the values entered define the *lower* thres
 in the screenshot above, the thresholds have been adjusted to suit the range of response times from the flight
 comparison website data, with values of 3000 or more displayed in red.
 
+It is not yet possible to alter the number of color bands, nor the colors used for each range.
+
 ### Tooltip formatting
 
 By default, the value shown in the tooltip when hovering over a band in the swimlane is shown to one decimal