[doc] aggregatord: add section CSV format

doc/owlps-aggregatord.t2t

@@ -84,6 +84,37 @@ the **-K** option).
 
 
 
+= CSV format =
+
+The text output is constituted of fields separated by semicolons (;).
+(We call it CSV format even though semicolons are used instead of
+commas.) The format can evolve from one version of OwlPS to another,
+this is why the first field of each line is the version of the format
+used. In the current version of the format, each line contains the
+following fields:
+
+- CSV format version = 1
+- MAC address of the transmitter
+- request type
+- number of packets sent by the transmitter
+- timestamp (transmission time at the transmitter), under the form
+  “seconds.nanoseconds”
+- X coordinate
+- Y coordinate
+- Z coordinate
+- direction (orientation) of the transmitter
+- one or more per-packet information made of the following fields:
+  - MAC address of the capture point
+  - packet ID
+  - signal strength
+
+
+If unknown, the coordinates are set to “0.00” and the orientation to
+“0”.
+
+
+
+
 = Options =
 
 == Main options ==