Added support for `bash-it help completions` command.

It's showing the same output as `bash-it show completions`,
to keep things simple.

completion/available/bash-it.completion.bash

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

lib/helpers.bash

@@ -285,6 +285,14 @@ _enable-thing ()
     printf '%s\n' "$file_entity enabled."
 }
 
+_help-completions()
+{
+  _about 'summarize all completions available in bash-it'
+  _group 'lib'
+
+  _bash-it-completions
+}
+
 _help-aliases()
 {
     _about 'shows help for all aliases, or a specific alias group'