cvsserver: Don't lie about binary mode in asciidoc documentation

The git-cvsserver documentation claims that the server will set
-k modes if appropriate which is not really the case. On the other
hand the available gitcvs.allbinary variable is not documented at
all. Fix both these issues by rewording the related paragraph.

Signed-off-by: Frank Lichtenheld <frank@lichtenheld.de>
Signed-off-by: Junio C Hamano <junkio@cox.net>

Documentation/git-cvsserver.txt

@@ -134,9 +134,11 @@ checkout, diff, status, update, log, add, remove, commit.
 Legacy monitoring operations are not supported (edit, watch and related).
 Exports and tagging (tags and branches) are not supported at this stage.
 
-The server will set the -k mode to binary when relevant. In proper GIT
+The server should set the -k mode to binary when relevant, however,
-tradition, the contents of the files are always respected.
+this is not really implemented yet. For now, you can force the server
-No keyword expansion or newline munging is supported.
+to set `-kb` for all files by setting the `gitcvs.allbinary` config
+variable. In proper GIT tradition, the contents of the files are
+always respected. No keyword expansion or newline munging is supported.
 
 Dependencies
 ------------