DOC: config: Fix 'http-response send-spoe-group' documentation

Arguments were missing in the rule heading. This patch may be backported as
far as 2.0.

(cherry picked from commit 24e7f354e9ccf292eb4404e7e50b87b5b0a61ccd)
Signed-off-by: Willy Tarreau <w@1wt.eu>
diff --git a/doc/configuration.txt b/doc/configuration.txt
index d28de2f..7a3961e 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -7244,7 +7244,8 @@
   boolean. If an error occurs, this action silently fails and the actions
   evaluation continues.
 
-http-response send-spoe-group [ { if | unless } <condition> ]
+http-response send-spoe-group <engine-name> <group-name>
+                              [ { if | unless } <condition> ]
 
   This action is used to trigger sending of a group of SPOE messages. To do so,
   the SPOE engine used to send messages must be defined, as well as the SPOE