Documentation/git-commit: rephrase the "initial-ness" of templates

The description of "commit -t <file>" said the file is used "as the
initial version" of the commit message, but in the context of an SCM,
"version" is a loaded word that can needlesslyl confuse readers.

Explain the purpose of the mechanism without using "version".

Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-commit.txt

@@ -132,11 +132,14 @@ OPTIONS
 
 -t <file>::
 --template=<file>::
-	Use the contents of the given file as the initial version of the
-	commit message. The editor is invoked so you can make subsequent
-	changes. If you make no changes, the commit is aborted. If a message
-	is specified using the `-m` or `-F` options, this option has no
-	effect. This overrides the `commit.template` configuration variable.
+	When editing the commit message, start the editor with the
+	contents in the given file.  The `commit.template` configuration
+	variable is often used to give this option implicitly to the
+	command.  This mechanism can be used by projects that want to
+	guide participants with some hints on what to write in the message
+	in what order.  If the user exits the editor without editing the
+	message, the commit is aborted.  This has no effect when a message
+	is given by other means, e.g. with the `-m` or `-F` options.
 
 -s::
 --signoff::