Add valideer to Data Validation

Author: gsakkis

README.md

@@ -586,6 +586,7 @@ A curated list of awesome Python frameworks, libraries and software. Inspired by
 * [schema](https://github.com/halst/schema) - A library for validating Python data structures.
 * [Schematics](https://github.com/schematics/schematics) - Data Structure Validation.
 * [kmatch](https://github.com/ambitioninc/kmatch) - A language for matching/validating/filtering Python dictionaries.
+* [valideer](https://github.com/podio/valideer) - Lightweight extensible data validation and adaptation library.
 
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