Fix shell autocomplete

Author: bcessa

cmd/completion.go

@@ -11,7 +11,7 @@ Before using completion features, you have to source completion code
 from your .profile or .bashrc/.zshrc file. This is done by adding
 following line to one of above files:
 
-	source <(tred completion SHELL)
+	source <(tredctl completion SHELL)
 
 Bash users can as well save it to the file and copy it to:
 	/etc/bash_completion.d/

cmd/root.go

@@ -9,7 +9,7 @@ import (
 )
 
 var rootCmd = &cobra.Command{
-	Use:   "tred",
+	Use:   "tredctl",
 	Short: "CLI for the 'Tamper Resistant Encrypted Data' protocol",
 }