add onion configuration library (#2821)

README.md

@@ -292,6 +292,7 @@ Please take a quick gander at the [contribution guidelines](https://github.com/a
 * [konfig](https://github.com/lalamove/konfig) - Composable, observable and performant config handling for Go for the distributed processing era.
 * [mini](https://github.com/sasbury/mini) - Golang package for parsing ini-style configuration files.
 * [nasermirzaei89/env](https://github.com/nasermirzaei89/env) - Simple useful package for read environment variables.
+* [onion](http://github.com/goraz/onion) - Layer based configuration for Go, Supports JSON, TOML, YAML, properties, etcd, env, and encryption using PGP.
 * [sprbox](https://github.com/oblq/sprbox) - Build-environment aware toolbox factory and agnostic config parser (YAML, TOML, JSON and Environment vars).
 * [store](https://github.com/tucnak/store) - Lightweight configuration manager for Go.
 * [viper](https://github.com/spf13/viper) - Go configuration with fangs.