Added a link to Gitter chat

Author: amologoko

README.md

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 # fix-simple-binary-encoding
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+[![Join the chat at https://gitter.im/fix-simple-binary-encoding/Lobby](https://badges.gitter.im/fix-simple-binary-encoding/Lobby.svg)](https://gitter.im/fix-simple-binary-encoding/Lobby?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
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 This project contains specifications and resources for Simple Binary Encoding (SBE).
 SBE is a FIX standard for binary message encoding.