Add first files for system internals documentation

[ci skip]

docs/internals/general_arch.md

+---
+title:  "General Architecture and Process Model"
+---
+
+<img src="projects_dependencies.svg" alt="The Flink sub-projects and their dependencies" height="400px"/>
+
+
+<img src="stack.svg" alt="The Flink component stack" height="400px"/>

docs/internals/overview.md

+---
+title:  "Overview of Flink System Architecture & Internals"
+---
+
+# Overview
+
+This documentation provides an overview of the architecture of the Flink system
+and its components. It is intended as guide to contributors, and people
+that are interested in the technology behind Flink.
+
+*This documentation is maintained by the contributors of the individual components.
+We kindly ask anyone that adds and changes components to eventually provide a patch
+or pull request that updates these documents as well.*
+
+
+### Architectures and Components
+
+- [General Architecture and Process Model](general_arch.html)
+
+- [Life Cycle of a Program](program_life_cycle.html)
+
+- [Jobs and Scheduling](job_scheduling.html)
+
+- [Distributed Runtime](distributed_runtime.html)
+
+- [Runtime Algorithms and Memory Management](distributed_runtime.html)
+
+- [Program Optimizer](optimizer.html)
+
+- [How-to: Adding a new Operator](add_operator.html)
+
+<!--
+- [Java API, Types, and Type Extraction](types.html)
+-->
+
+<!--
+- [RPC and JobManager Communication](rpc_transfer.html)
+-->
+