[docs] Adds documentation on setup of intelliJ

[docs] Links internal_setup_intellij.html from internal_howto.html

This closes #480

docs/internal_howto.md

@@ -33,6 +33,8 @@ that are interested in the technology behind Flink.
 
 - [How-to: Setting up Eclipse to develop Flink](internal_setup_eclipse.html)
 
+- [How-to: Setting up IntelliJ to develop Flink](internal_setup_intellij.html)
+
 ---
 
 *This documentation is maintained by the contributors of the individual components.

docs/internal_setup_intellij.md

+---
+title:  "How to set up IntelliJ IDEA"
+---
+<!--
+Licensed to the Apache Software Foundation (ASF) under one
+or more contributor license agreements.  See the NOTICE file
+distributed with this work for additional information
+regarding copyright ownership.  The ASF licenses this file
+to you under the Apache License, Version 2.0 (the
+"License"); you may not use this file except in compliance
+with the License.  You may obtain a copy of the License at
+
+  http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing,
+software distributed under the License is distributed on an
+"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+KIND, either express or implied.  See the License for the
+specific language governing permissions and limitations
+under the License.
+-->
+
+
+
+A brief guide on how to set up IntelliJ IDEA IDE for development of the Flink core.
+As Eclipse is known to have issues with mixed Scala and Java projects, more and more contributers are migrating to IntelliJ IDEA.
+
+The following documentation describes the steps to setup IntelliJ IDEA 14.0.3 (https://www.jetbrains.com/idea/download/) with the Flink sources.
+
+Prior to doing anything, make sure that the Flink project is built at least once from the terminal:
+`mvn clean package -DskipTests`
+
+# IntelliJ IDEA
+
+## Installing the Scala plugin
+1. Go to IntelliJ plugins settings (File -> Settings -> Plugins) and click on "Install Jetbrains plugin...". 
+2. Select and install the "Scala" plugin. 
+3. Restart IntelliJ
+
+## Installing the Scala compiler plugin
+1. Go to IntelliJ scala compiler settings (File -> Settings -> Build, Execution, Deployment -> Compiler -> Scala Compiler) and click on "Install Jetbrains plugin...". 
+2. Click on the green plus icon on the right to add a compiler plugin
+3. Point to the paradise jar: ~/.m2/repository/org/scalamacros/paradise_2.10.4/2.0.1/paradise_2.10.4-2.0.1.jar If there is no such file, this means that you should build Flink from the terminal as explained above.
+
+## Importing Flink
+1. Start IntelliJ IDEA and choose "Import Project"
+2. Select the root folder of the Flink repository
+3. Choose "Import project from external model" and select "Maven"
+4. Leave the default options and finish the import.
+
+---
+
+*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.*
+