Adds a bit of text to explain that the "event" file for acme doesn't take the same format for input
written to the file as it outputs.

Based on the function I posted to 9fans a few days ago for "winclear".

Notes:
Sat Aug 12 02:34:38 EDT 2006 rsc
    I think that section is perfectly clear.
    It's only talking about the so-called output messages.
    (One man's output is another man's input, of course.)
    At the end of the section it does talk about which 
    messages can be written back, and what format they must take.
    


Reference: /n/sources/patch/sorry/acme4-event-description-clarification
Date: Mon Jul 17 08:20:57 CES 2006
Signed-off-by: leimy@plan9.jp
Reviewed-by: rsc

--- /sys/man/4/acme	Mon Jul 17 08:17:27 2006
+++ /sys/man/4/acme	Mon Jul 17 08:17:24 2006
@@ -341,11 +341,16 @@
 it is expected that the program reading the
 .B event
 file will interpret them.
-The messages have a fixed format:
+The output messages have a fixed format:
 a character indicating the origin or cause of the action,
 a character indicating the type of the action,
 four free-format blank-terminated decimal numbers,
 optional text, and a newline.
+.BR
+The input messages have the following format:
+a character indicating the origin or cause of the action,
+a character indicating the type of the action,
+two free-format blank-terminated decimal numbers, and a newline
 The first and second numbers are the character addresses of the action,
 the third is a flag,
 and the final is a count of the characters in the optional text, which