Rework scp.

* No double examples
 * Replace IP address with hostname place holders.
 * change word use to avoid upload & download
 * alter two remote hosts example, to not require agent forwarding.

Add SFTP examples.

pages/common/sftp.md

@@ -0,0 +1,20 @@
+# sftp
+
+> Secure file transfer program.
+> Copy files between hosts using Secure File Transfer Protocol over SSH.
+
+- Connect to a remote server and enter an interactive command mode:
+
+`sftp {{remote_user}}@{{remote_host}}`
+
+- Connect using an alternate port:
+
+`sftp -P {{remote_port}} {{remote_host}}`
+
+- Copy a local file to a remote host:
+
+`sftp {{local_file}} {{remote_host}}:{{/path/remote_file}}`
+
+- Copy a remote file to the local host:
+
+`sftp {{remote_host}}:{{/path/remote_file}} {{local_file}}`