Update README.md: social media and more
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-Contiki-NG is a fork of Contiki, with focus on next generation IoT protocols and platforms: http://contiki-ng.org
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-Documentation is available on the wiki: https://github.com/contiki-ng/contiki-ng/wiki
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+Contiki-NG is a fork of Contiki, with focus on next generation IoT protocols and platforms.
+Important links:
+* GitHub repository: https://github.com/contiki-ng/contiki-ng
+* Documentation: https://github.com/contiki-ng/contiki-ng/wiki
+* Gitter: https://gitter.im/contiki-ng
+* Twitter: https://twitter.com/contiki_ng
+* Web site: http://contiki-ng.org
