Add completion for help command, and help for migrate

completion/available/bash-it.completion.bash

@@ -61,7 +61,7 @@ _bash-it-comp()
 			return 0
 			;;
 		help)
-			local help_args="plugins aliases completions update"
+			local help_args="plugins aliases completions migrate update"
 			COMPREPLY=( $(compgen -W "${help_args}" -- ${cur}) )
 			return 0
 			;;

lib/helpers.bash

@@ -469,6 +469,14 @@ _help-update () {
   echo "Check for a new version of Bash-it and update it."
 }
 
+_help-migrate () {
+  _about 'help message for migrate command'
+  _group 'lib'
+
+  echo "Migrates internal Bash-it structure to the latest version in case of changes."
+  echo "The 'migrate' command is run automatically when calling 'update', 'enable' or 'disable'."
+}
+
 all_groups ()
 {
     about 'displays all unique metadata groups'