Update guidelines for contributing.

Let "GitHub" users see the project's policy.

CONTRIBUTING.md

@@ -25,7 +25,7 @@
  | commons-build-plugin/trunk/src/main/resources/commons-xdoc-templates |
  +======================================================================+
  |                                                                      |
- | 1) Re-generate using: mvn commons:contributing-md                    |
+ | 1) Re-generate using: mvn commons-build:contributing-md              |
  |                                                                      |
  | 2) Set the following properties in the component's pom:              |
  |    - commons.jira.id  (required, alphabetic, upper case)             |
@@ -50,53 +50,66 @@ Getting Started
 
 + Make sure you have a [JIRA account](https://issues.apache.org/jira/).
 + Make sure you have a [GitHub account](https://github.com/signup/free).
-+ If you're planning to implement a new feature it makes sense to discuss you're changes on the [dev list](https://commons.apache.org/mail-lists.html) first. This way you can make sure you're not wasting your time on something that isn't considered to be in Apache Commons Math's scope.
-+ Submit a ticket for your issue, assuming one does not already exist.
++ If you're planning to implement a new feature it makes sense to discuss your changes on the [dev list](https://commons.apache.org/mail-lists.html) first. This way you can make sure you're not wasting your time on something that isn't considered to be in Apache Commons Math's scope.
++ Submit a [Jira Ticket][jira] for your issue, assuming one does not already exist.
   + Clearly describe the issue including steps to reproduce when it is a bug.
   + Make sure you fill in the earliest version that you know has the issue.
-+ Fork the repository on GitHub.
++ Find the corresponding [repository on GitHub](https://github.com/apache/?query=commons-),
+[fork](https://help.github.com/articles/fork-a-repo/) and check out your forked repository.
 
 Making Changes
 --------------
 
-+ Create a topic branch from where you want to base your work (this is usually the develop/trunk branch).
++ Create a _topic branch_ for your isolated work.
+  * Usually you should base your branch on the `master` or `trunk` branch.
+  * A good topic branch name can be the JIRA bug id plus a keyword, e.g. `MATH-123-InputStream`.
+  * If you have submitted multiple JIRA issues, try to maintain separate branches and pull requests.
 + Make commits of logical units.
+  * Make sure your commit messages are meaningful and in the proper format. Your commit message should contain the key of the JIRA issue.
+  * e.g. `MATH-123: Close input stream earlier`
 + Respect the original code style:
   + Only use spaces for indentation.
-  + Create minimal diffs - disable on save actions like reformat source code or organize imports. If you feel the source code should be reformatted create a separate PR for this change.
-  + Check for unnecessary whitespace with git diff --check before committing.
-+ Topic branch names should directly correspond to the JIRA issues they are intended to resolve. For example branch names should look like:
-  + `improvement-MATH-852`
-  + `bug-MATH-1329`
-  + `feature-MATH-621`
-+ Make sure your commit messages are in the proper format. Your commit message should contain the key of the JIRA issue.
-  + For example, a commit message might look like `MATH-852: Adding documentation for development`
-+ Make sure you have added the necessary tests for your changes.
+  + Create minimal diffs - disable _On Save_ actions like _Reformat Source Code_ or _Organize Imports_. If you feel the source code should be reformatted create a separate PR for this change first.
+  + Check for unnecessary whitespace with `git diff` -- check before committing.
++ Make sure you have added the necessary tests for your changes, typically in `src/test/java`.
 + Run all the tests with `mvn clean verify` to assure nothing else was accidentally broken.
 
 Making Trivial Changes
 ----------------------
 
+The JIRA tickets are used to generate the changelog for the next release.
+
 For changes of a trivial nature to comments and documentation, it is not always necessary to create a new ticket in JIRA.
 In this case, it is appropriate to start the first line of a commit with '(doc)' instead of a ticket number.
 
+
 Submitting Changes
 ------------------
 
-+ Sign the [Contributor License Agreement][cla] if you haven't already.
++ Sign and submit the Apache [Contributor License Agreement][cla] if you haven't already.
+  * Note that small patches & typical bug fixes do not require a CLA as
+    clause 5 of the [Apache License](https://www.apache.org/licenses/LICENSE-2.0.html#contributions)
+    covers them.
 + Push your changes to a topic branch in your fork of the repository.
-+ Submit a pull request to the repository in the apache organization.
++ Submit a _Pull Request_ to the corresponding repository in the `apache` organization.
+  * Verify _Files Changed_ shows only your intended changes and does not
+  include additional files like `target/*.class`
 + Update your JIRA ticket and include a link to the pull request in the ticket.
 
+If you prefer to not use GitHub, then you can instead use
+`git format-patch` (or `svn diff`) and attach the patch file to the JIRA issue.
+
+
 Additional Resources
 --------------------
 
 + [Contributing patches](https://commons.apache.org/patches.html)
-+ [Apache Commons Math JIRA project page](https://issues.apache.org/jira/browse/MATH)
++ [Apache Commons Math JIRA project page][jira]
 + [Contributor License Agreement][cla]
 + [General GitHub documentation](https://help.github.com/)
-+ [GitHub pull request documentation](https://help.github.com/send-pull-requests/)
++ [GitHub pull request documentation](https://help.github.com/articles/creating-a-pull-request/)
 + [Apache Commons Twitter Account](https://twitter.com/ApacheCommons)
-+ #apachecommons IRC channel on freenode.org
++ `#apache-commons` IRC channel on `irc.freenode.net`
 
 [cla]:https://www.apache.org/licenses/#clas
+[jira]:https://issues.apache.org/jira/browse/MATH