[PATCH] Doc fix for git-reflog: mention @{...} syntax, and <ref> in synopsys.

[Matthieu Moy <Matthieu.Moy@imag.fr>]

The HEAD@{...} syntax was documented in git-rev-parse manpage, which
is hard to find by someone looking for the documentation of porcelain.
git-reflog is probably the place where one expects to find this.

While I'm there, "git revlog show whatever" was also undocumented.
---
 Documentation/git-reflog.txt |   11 +++++++++--
 1 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/Documentation/git-reflog.txt b/Documentation/git-reflog.txt
index 5c7316c..aeac6f0 100644
--- a/Documentation/git-reflog.txt
+++ b/Documentation/git-reflog.txt
@@ -19,7 +19,7 @@ depending on the subcommand:
 git reflog expire [--dry-run] [--stale-fix] [--verbose]
 	[--expire=<time>] [--expire-unreachable=<time>] [--all] <refs>...
 
-git reflog [show] [log-options]
+git reflog [show] [log-options] [<ref>]
 
 Reflog is a mechanism to record when the tip of branches are
 updated.  This command is to manage the information recorded in it.
@@ -32,10 +32,17 @@ directly by the end users -- instead, see gitlink:git-gc[1].
 
 The subcommand "show" (which is also the default, in the absence of any
 subcommands) will take all the normal log options, and show the log of
-`HEAD`, which will cover all recent actions, including branch switches.
+`HEAD`, or of the reference provided in the command-line, which will
+cover all recent actions, including branch switches.
 It is basically an alias for 'git log -g --abbrev-commit
 --pretty=oneline', see gitlink:git-log[1].
 
+The reflog is useful in various git commands, to specify the old value
+of a reference. For example, `HEAD@\{2\}` means "where HEAD used to be
+two moves ago", `master@\{one.week.ago\}` means "where master used to
+point to one week ago", and so on. See gitlink:git-rev-parse[1] for
+more details.
+
 
 OPTIONS
 -------
-- 
1.5.3.5.724.g49d9d