Add an introduction.

index.rst

@@ -6,6 +6,17 @@
 Welcome to Limnoria's documentation!
 ====================================
 
+Limnoria is a robust (it doesn't crash), user friendly (it's easy to
+configure) and programmer friendly (plugins are *extremely* easy to write)
+Python IRC bot.
+It aims to be an adequate replacement for most existing IRC bots.
+It includes a very flexible and powerful ACL system for controlling access
+to commands, as well as more than 60 builtin plugins providing around 400
+actual commands.
+
+It is the successor of Supybot since 2010 and provides many new features,
+but keeps full compatibility with existing configurations and plugins.
+
 Contents:
 
 .. toctree::