Begin contributing document (jump-dev#1377)

* Begin contributing document

* Improve contributing guidelines

* Respond to comments

* Minor changes to contributing document

* Add code of conduct to contributing guide

* Minor changes

* Move contributing back to root

* Respond to Benoit

* Respond to Mohamed

CODE_OF_CONDUCT.md

@@ -34,10 +34,9 @@ aware that most community members contribute on a voluntary basis, so ideas and
 bug reports are ok, but demands are not. Along these lines, it's important to
 keep in mind that, unless stated otherwise, JuMP's interfaces to commercial
 solvers are maintained by volunteers who find them useful. Pull requests are
-always welcomed. We haven't yet put together a guide for new contributors, but
-please reach out in the [developer
-chatroom](https://gitter.im/JuliaOpt/JuMP-dev) with questions about how to get
-started.
+always welcomed. Please check out our [contributing guide](https://github.com/JuliaOpt/JuMP.jl/blob/master/CONTRIBUTING.md).
+You can also reach out in the [developer chatroom](https://gitter.im/JuliaOpt/JuMP-dev)
+with questions about how to get started.
 
 ## Any concerns?
 

CONTRIBUTING.md

@@ -0,0 +1,80 @@
+# How to contribute to JuMP
+
+Welcome! This document explains some of the ways you can contribute to JuMP.
+
+## Code of Conduct
+
+This project and everyone participating in it is governed by the
+[JuMP Code of Conduct](https://github.com/JuliaOpt/JuMP.jl/blob/master/CODE_OF_CONDUCT.md).
+By participating, you are expected to uphold this code.
+
+## Join the Discourse forum
+
+First up, join the [Discourse forum](https://discourse.julialang.org/c/domain/opt).
+
+The forum is a good place to ask questions about how to use JuMP. You can also
+use the forum to discuss possible feature requests and bugs before raising a
+Github issue (more on this below).
+
+Aside from asking questions, the easiest way you can contribute to JuMP is to
+help answer questions on Discourse!
+
+## Improve the documentation
+
+Chances are, if you asked (or answered) a question on Discourse, then it is
+usually a sign that the [documentation](http://www.juliaopt.org/JuMP.jl/latest/)
+could be improved. Moreover, since it is your question, you are probably the
+best-placed person to improve it!
+
+The docs are written in Markdown and are built using [Documenter.jl](https://github.com/JuliaDocs/Documenter.jl).
+You can find the source of all the docs [here](https://github.com/JuliaOpt/JuMP.jl/tree/master/docs).
+
+If your change is small (like fixing typos, or one or two sentence corrections),
+the easiest way to do this is via Github's online editor. (Github has
+[help](https://help.github.com/articles/editing-files-in-another-user-s-repository/)
+on how to do this.)
+
+If your change is larger, or touches multiple files, you will need to make the
+change locally and then use Git to submit a pull request. (See *Contribute code
+to JuMP* below for more on this.)
+
+If you need any help, come join our [Gitter](https://gitter.im/JuliaOpt/JuMP-dev)
+channel and we will walk you through the process.
+
+## File a bug report
+
+A third way to contribute to JuMP is to file [bug reports](https://github.com/JuliaOpt/JuMP.jl/issues/new?template=bug_report.md).
+
+Make sure you read the info in the box where you write the body of the issue
+before posting. You can also find a copy of that info [here](https://github.com/JuliaOpt/JuMP.jl/blob/master/.github/ISSUE_TEMPLATE/bug_report.md).
+
+## Contribute code to JuMP
+
+Finally, you can also contribute code to JuMP!
+
+If you do not have experience with Git, Github, and Julia development, the first
+steps can be a little daunting. However, there are lots of tutorials available
+online (such as [this](http://try.github.io/), [this](https://guides.github.com/activities/hello-world/),
+[this](https://git-scm.com/book/en/v2), and [this](https://docs.julialang.org/en/stable/manual/packages/#Making-changes-to-an-existing-package-1)).
+If you need any help, come join our [Gitter](https://gitter.im/JuliaOpt/JuMP-dev)
+channel and we will walk you through the process.
+
+Once you are familiar with Git, the workflow for contributing code to JuMP is
+along the lines of the following:
+1. Find an [open issue](https://github.com/JuliaOpt/JuMP.jl/issues) (or open a
+    new one) for the problem you want to solve
+2. Discuss (in the issue, or on [Gitter](https://gitter.im/JuliaOpt/JuMP-dev))
+    _before_ spending too much time on it to test the waters first and see if
+    other contributors are fine with your proposed changes
+3. Make your changes locally. (The Julia manual has a [guide](https://docs.julialang.org/en/stable/manual/packages/#Making-changes-to-an-existing-package-1)
+    on how to do this.) Make sure you:
+    - Follow the [style guide](http://www.juliaopt.org/JuMP.jl/latest/style.html)
+    - Add tests and documentation for any changes or new features
+4. Submit a pull request to Github
+5. Update your pull request, responding to any comments
+
+Remember to be patient and polite; you may get a _lot_ of comments on your pull
+request! However, do not be afraid! A lot of comments means that people are
+willing to help you improve the code that you are contributing to JuMP.
+
+Thanks for contributing to JuMP!