adding beam doc

Author: pulasthi

docs/docs/compatibility/beam.md

@@ -0,0 +1,44 @@
+---
+id: apachebeam
+title: Apache Beam Runner
+sidebar_label: Apache Beam
+---
+
+
+Apache Beam is an open source, unified model for defining both batch and streaming data-parallel processing pipelines.
+Beam provides several open sources SDK's which can he used to build a pipline. This pipline is then 
+executed using one of the many distributed processing back-ends supported by Apache beam. Currently 
+Frameworks such as Apache Spark and Apache Flink are supported, these are called runners.
+
+Twister2 has a Apache Beam runner that is currently being shipped with the Twister2 release, which we plan to 
+include directly into Apache Beam, This runner allows users to run Apache beam piplines with Twister2
+
+Below is an example code that runs a Beam pipline using Twister2 Runner
+
+```java
+    Twister2PipelineOptions options = PipelineOptionsFactory.as(Twister2PipelineOptions.class);
+    options.setTSetEnvironment(env);
+    options.as(Twister2PipelineOptions.class).setRunner(Twister2LegacyRunner.class);
+    String resultPath = "/home/pulasthi/work/twister2/beamtest/testdir";
+    Pipeline p = Pipeline.create(options);
+    PCollection<String> result =
+        p.apply(GenerateSequence.from(0).to(10))
+            .apply(
+                ParDo.of(
+                    new DoFn<Long, String>() {
+                      @ProcessElement
+                      public void processElement(ProcessContext c) throws Exception {
+                        c.output(c.element().toString());
+                      }
+                    }));
+
+    try {
+      result.apply(TextIO.write().to(new URI(resultPath).getPath() + "/part"));
+    } catch (URISyntaxException e) {
+      LOG.info(e.getMessage());
+    }
+    p.run();
+```
+
+Apache beam provides a rich set of SDK's with many adapters which allow you to integrate with
+various systems, you can learn more about Apache Beam by referring the Apache Beam [documentation](https://beam.apache.org/documentation/).