add -J proxyjump option (#15)

doc/mscp.1.in

@@ -56,6 +56,9 @@ mscp \- copy files over multiple SSH connections
 .BI \-i \ IDENTITY\c
 ]
 [\c
+.BI \-J \ DESTINATION\c
+]
+[\c
 .BI \-c \ CIPHER\c
 ]
 [\c
@@ -270,6 +273,19 @@ supports.
 .B \-i \fIIDENTITY\fR
 Specifies the identity file for public key authentication.
 
+.TP
+.B \-J \fIDESTINATION\fR
+A shortcut to define a
+.B ProxyJump
+configuration directive. Each SFTP session of
+.B mscp
+connects to the target host by first making an
+.B ssh
+connection to the jump host described by
+.I destination.
+
+
+
 .TP
 .B \-c \fICIPHER\fR
 Selects the cipher to use for encrypting the data transfer. See