a quick explanation of the format

docs/sphinx/source/format/index.rst

@@ -4,3 +4,13 @@
 
 Avatar ENSignes uses its own format to represent and manipulate signs, written
 in the YaML markup langage.
+
+The main idea of this format is to divide a sign into fixed *states*
+(configurations of the hands at a given time) and to describe the sign as
+transitions between these states.
+
+.. toctree::
+   :maxdepth: 1
+			  
+   example
+   conventions