Docs edit, noted double backslash requirement for some regex operators (#1361)

docs/scarpet/language/SystemFunctions.md

@@ -205,10 +205,11 @@ title('aBc') => 'Abc'
 ### `replace(string, regex, repl?); replace_first(string, regex, repl?)`
 
 Replaces all, or first occurence of a regular expression in the string with `repl` expression, 
-or nothing, if not specified
+or nothing, if not specified. To use escape characters (`\(`,`\+`,...), metacharacters (`\d`,`\w`,...), or position anchors (`\b`,`\z`,...) in your regular expression, use two backslashes.
 
 <pre>
 replace('abbccddebfg','b+','z')  // => azccddezfg
+replace('abbccddebfg','\\w$','z')  // => abbccddebfz
 replace_first('abbccddebfg','b+','z')  // => azccddebfg
 </pre>