update README file

Author: TimothyYe

README.md

@@ -73,7 +73,7 @@ COMMANDS:
      delete, d    Delete specific SSH key by alias name.
      rename, rn   Rename SSH key alias name to a new one.
      copy, cp     Copy current SSH public key to a remote host.
-     display, dp  Display the current SSH public key or specific public key by alias name.
+     display, dp  Display the current SSH public key or specific SSH public key by alias name.
      backup, b    Backup all SSH keys to an archive file.
      restore, r   Restore SSH keys from an existing archive file.
      help, h      Shows a list of commands or help for one command.