README: add image to configuration doc

Author: Lukas955

doc/sphinx/configuration.rst

@@ -1,6 +1,10 @@
 Collector configuration
 =======================
 
+.. image:: img/configuration.svg
+    :width: 60%
+    :align: right
+
 IPFIXcol is designed to be easily extensible by input, intermediate and output plugins.
 Therefore, the startup configuration of the collector consists of 3 parts, each for one type of
 plugins, as illustrated below. The collector typically receives data from exporters and stores
@@ -193,4 +197,4 @@ Even instances of the same plugin can run concurrently. However, instances must
 different configurations. For example, instances of output plugins should not write to the same
 directory, instances of input plugins cannot listen on the same port and interface, etc.
 
-Just like everywhere else your collector is as fast as the slowest plugin in the configuration.
+Just like everywhere else your collector is as fast as the slowest plugin in the configuration.