Add completion.get_trigger_characters as configurable option

README.md

@@ -187,6 +187,11 @@ length of the word to the left of the cursor is less than `keyword_length`.
 
 Default: `1`
 
+### completion.get_trigger_characters (type: fun(trigger_characters: string[]): string[])
+
+The function to resolve trigger_characters.
+
+Default: `function(trigger_characters) return trigger_characters end`
 
 #### completion.completeopt (type: string)