Add 'git bisect replay/log' documentation.

... lest I get yelled at by a very angry scm ;-).
Signed-off-by: NJunio C Hamano <junkio@cox.net>

Documentation/git-bisect.txt

@@ -13,7 +13,8 @@ SYNOPSIS
 'git bisect' good <rev>
 'git bisect' reset [<branch>]
 'git bisect' visualize
-
+'git bisect' replay <logfile>
+'git bisect' log
 
 DESCRIPTION
 -----------
@@ -75,6 +76,15 @@ During the bisection process, you can say
 
 to see the currently remaining suspects in `gitk`.
 
+The good/bad you told the command is logged, and `git bisect
+log` shows what you have done so far.  You can truncate its
+output somewhere and save it in a file, and run
+
+	git bisect replay that-file
+
+if you find later you made a mistake telling good/bad about a
+revision.
+
 
 Author
 ------