Update documentation for :Git {args} command

Added description for multifile edit behavior.

Author: Fabian Wermelinger

doc/fugitive.txt

@@ -29,8 +29,10 @@ that are part of Git repositories).
                         On UNIX this uses a pty and on other platforms it uses
                         a pipe, which will cause some behavior differences
                         such as the absence of progress bars.  Any file the
-                        command edits (for example, a commit message) will be
-                        loaded into a split window.  Closing that window will
+                        command edits (for example, a commit message or email
+                        drafts for multiple patches) will be loaded into a
+                        split window for each file to edit.  Closing that
+                        window (or the last window for multifile edits) will
                         resume running the command.  A few Git subcommands
                         have different behavior; these are documented below.