added production users and integrations pages

Documentation/integrations.md

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+# Integrations
+This document tracks the libraries and tools that are compatible with flannel. [Join the community](https://github.com/coreos/flannel/), and help us keep the list up-to-date.
+
+## Tools
+
+## Projects with a flannel dependency

Documentation/production-users.md

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+# Production users
+
+This document tracks people and use cases for flannel in production. [Join the community](https://github.com/coreos/flannel/), and help us keep the list up-to-date.