Updated README to include new numerical validators

Author: jamsidedown

README.md

@@ -45,6 +45,8 @@ Currently, the package offers 3 validators:
 * [__Mandatory__](https://github.com/gridsmartercities/aws-lambda-decorators/blob/master/aws_lambda_decorators/validators.py#L5-L16): Checks if a parameter has a value.
 * [__RegexValidator__](https://github.com/gridsmartercities/aws-lambda-decorators/blob/master/aws_lambda_decorators/validators.py#L19-L38): Checks a parameter against a regular expression.
 * [__SchemaValidator__](https://github.com/gridsmartercities/aws-lambda-decorators/blob/master/aws_lambda_decorators/validators.py#L41-L63): Checks if an object adheres to the schema. Uses [schema](https://github.com/keleshev/schema) library.
+* [__Minimum__](https://github.com/gridsmartercities/aws-lambda-decorators/blob/master/aws_lambda_decorators/validators.py#L66-L91): Checks if an optional numerical value is greater than a minimum value.
+* [__Maximum__](https://github.com/gridsmartercities/aws-lambda-decorators/blob/master/aws_lambda_decorators/validators.py#L94-L119): Checks if an optional numerical value is less than a maximum value.
 
 ### [Decoders](https://github.com/gridsmartercities/aws-lambda-decorators/blob/master/aws_lambda_decorators/decoders.py)