(#2183) updated str2bool readme wording

Author: marrero984

README.markdown

@@ -711,7 +711,7 @@ Returns a new string where runs of the same character that occur in this set are
 
 #### `str2bool`
 
-Converts a string to a boolean regardless of case. This attempts to convert strings that contain values such as '1', 't', 'y', 'Y', 'YES','yes', and 'TRUE' to 'true' and strings that contain values such as '0', 'f','F', 'N','n', 'NO','FALSE', and 'no' to 'false'. *Type*: rvalue.  
+Converts certain strings to a boolean. This attempts to convert strings that contain the values '1', 't', 'y', and 'yes' to 'true'.  Strings that contain values '0', 'f', 'n', and 'no', or are an an empty string or undefined are converted to 'false'. Any other value will cause an error. *Type*: rvalue.
 
 #### `str2saltedsha512`