Update CONTRIBUTING.md

Adding workflow instructions for contributing to Akka

CONTRIBUTING.md

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+#Contributing to Akka#
+
+Greetings traveller!
+
+##Infrastructure##
+
+* [Akka Contributor License Agreement](www.typesafe.com/contribute/cla)
+* [Akka Issue Tracker](http://doc.akka.io/docs/akka/current/project/issue-tracking.html)
+
+##Workflow##
+
+0. Sign the Akka Contributor License Agreement,
+   we won't accept anything from anybody who has not signed it.
+1. Find-or-create a ticket in the issue tracker
+2. Assign that ticket to yourself
+3. Create a local branch with the following name format: wip-X-Y
+   where the X is the number of the ticket in the tracker,
+   and Y is your initials or similar.
+4. Do what needs to be done (with tests and docs if applicable).
+   Your branch should pass all tests before going any further.
+5. Push the branch to your clone of the Akka repository
+6. Create a Pull Request onto the applicable Akka branch,
+   if the number of commits are more than a few, please squash the
+   commits first.
+7. Change the status of your ticket to "Test"
+8. The Pull Request will be reviewed by the Akka committers
+9. Modify the Pull Request as agreed upon during the review,
+   then push the changes to your branch in your Akka repository,
+   the Pull Request should be automatically updated with the new
+   content.
+10. Several cycles of review-then-change might occur.
+11. Pull Request is either merged by the Akka committers,
+    or rejected, and the associated ticket will be updated to
+    reflect that.
+12. Delete the local and remote wip-X-Y