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>
 
@@ -428,4 +429,4 @@ not present, and default expression is provided, sets a new value to be associat
 ### `system_variable_set(key, new_value)`
 
 Returns the variable from the system shared key-value storage keyed with a `key` value, and sets a new 
-mapping for the key
+mapping for the key