Documentation: do not use undefined terms git-dir and git-file

We will add gitfile to the glossary in a separate commit.

Signed-off-by: Thomas Ackermann <th.acker@arcor.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-rev-parse.txt

@@ -187,9 +187,11 @@ print a message to stderr and exit with nonzero status.
 	Flags and parameters to be parsed.
 
 --resolve-git-dir <path>::
-	Check if <path> is a valid git-dir or a git-file pointing to a valid
+	Check if <path> is a valid repository or a gitfile that
-	git-dir. If <path> is a valid git-dir the resolved path to git-dir will
+	points at a valid repository, and print the location of the
-	be printed.
+	repository.  If <path> is a gitfile then the resolved path
+	to the real repository is printed.
+
 
 include::revisions.txt[]