Setting up 'contrib' directory and rules.

----Release Notes----
[]
-------------
Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=87958147

CONTRIBUTING.md

@@ -19,7 +19,12 @@ frustration later on.
 
 ### Code reviews
 All submissions, including submissions by project members, require review. We
-use Github pull requests for this purpose.
+use GitHub pull requests for this purpose.
+
+### Organization
+During our review and triage of incoming pull requests, we'll advise whether to
+include your contribution into the mainline SDK, or to maintain it within the
+separate group of [community-contributed modules](https://github.com/GoogleCloudPlatform/DataflowJavaSDK/tree/master/contrib).
 
 ### The small print
 Contributions made by corporations are covered by a different agreement than

contrib/README.md

@@ -0,0 +1,53 @@
+# Community contributions
+
+This directory hosts a wide variety of community contributions that may be
+useful to other users of
+[Google Cloud Dataflow](https://cloud.google.com/dataflow/),
+but may not be appropriate or ready yet for inclusion into the
+[mainline SDK](https://github.com/GoogleCloudPlatform/DataflowJavaSDK/) or a
+separate Google-maintained artifact.
+
+## Organization
+
+Each subdirectory represents a logically separate and independent module.
+Preferably, the code is hosted directly in this repository. When appropriate, we
+are also open to linking external repositories via
+[`submodule`](http://git-scm.com/docs/git-submodule/) functionality within Git.
+
+While we are happy to host individual modules to provide additional value to all
+Cloud Dataflow users, the modules are _maintanted solely by their respective
+authors_. We will make sure that modules are related to Cloud Dataflow, that
+they are distributed under the same license as the mainline SDK, and provide
+some guidance to the authors to make the quality as high as possible.
+
+We __cannot__, however, provide _any_ guarantees about correctness,
+compatibility, performance, support, test coverage, maintenance or future
+availability of individual modules hosted here.
+
+## Process
+
+In general, we recommend to get in touch with us through the issue tracker
+first. That way we can help out and possibly guide you. Coordinating up front
+makes it much easier to avoid frustration later on.
+
+We welcome pull requests with a new module from everyone. Every module must be
+related to Cloud Dataflow and must have an informative README.md file. We will
+provide general guidance, but usually won't be reviewing the module in detail.
+We reserve the right to refuse acceptance to any module, or remove it at any
+time in the future.
+
+We also welcome improvements to an existing module from everyone. We'll often
+wait for comments from the primary author of the module before merging a pull
+request from a non-primary author.
+
+As the module matures, we may choose to pull it directly into the mainline SDK
+or promote it to a Google-managed artifact.
+
+## Licensing
+
+We require all contributors to sign the Contributor License Agreement, exactly
+as we require for any contributions to the mainline SDK. More information is
+available in our [CONTRIBUTING.md](https://github.com/GoogleCloudPlatform/DataflowJavaSDK/blob/master/CONTRIBUTING.md)
+file.
+
+_Thank you for your contribution to the Cloud Dataflow community!_