added gitter chat

Author: tonda-kriz

README.md

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 **simple data struct** serialization library for C++. With this library you can serialize and deserialize *POD* C++ structs directly to [JSON](https://json.org) or [protobuf](https://github.com/protocolbuffers/protobuf).
 When used together with [etl library](https://github.com/ETLCPP/etl) it doesn't need to allocate any memory, so its suitable for embedded environments (see [extensions](doc/extensions.md)).