Add a contribution guide to help those who help

CONTRIBUTING.md

@@ -0,0 +1,84 @@
+# Contributing to sharp
+
+Hello, thank you for your interest in helping!
+
+## Submit a new bug report
+
+Please create a [new issue](https://github.com/lovell/sharp/issues/new) containing the steps to reproduce the problem.
+
+New bugs are assigned a `triage` label whilst under investigation.
+
+If you're having problems with `npm install sharp`, please include the output of the following commands, perhaps as a [gist](https://gist.github.com/):
+
+```sh
+vips -v
+pkg-config --print-provides vips
+npm install --verbose sharp
+```
+
+## Submit a new feature request
+
+If a [similar request](https://github.com/lovell/sharp/labels/enhancement) exists, it's probably fastest to add a comment to it about your requirement.
+
+Implementation is usually straightforward if _libvips_ [already supports](http://www.vips.ecs.soton.ac.uk/supported/current/doc/html/libvips/ch03.html) the feature you need.
+
+## Submit a Pull Request to fix a bug
+
+Thank you! To prevent the problem occurring again, please add unit tests that would have failed.
+
+Please select the `master` branch as the destination for your Pull Request so your fix can be included in the next minor release.
+
+Please squash your changes into a single commit using a command like `git rebase -i upstream/master`.
+
+## Submit a Pull Request with a new feature
+
+Please add JavaScript [unit tests](https://github.com/lovell/sharp/tree/master/test/unit) to cover your new feature. A test coverage report for the JavaScript code is generated in the `coverage/lcov-report` directory.
+
+You deserve to add your details to the [list of contributors](https://github.com/lovell/sharp/blob/master/package.json#L5).
+
+Any change that modifies the existing public API should be added to the relevant work-in-progress branch for inclusion in the next major release.
+
+| Release | WIP branch |
+| ------: | :--------- |
+|  v0.9.0 | intake     |
+| v0.10.0 | judgement  |
+| v0.11.0 | knife      |
+
+Please squash your changes into a single commit using a command like `git rebase -i upstream/<wip-branch>`.
+
+### Add a new public method
+
+The API tries to be as fluent as possible. Image processing concepts follow the naming conventions from _libvips_ and, to a lesser extent, _ImageMagick_.
+
+Most methods have optional parameters and assume sensible defaults. Methods with mandatory parameters often have names like `doSomethingWith(X)`.
+
+Please ensure backwards compatibility where possible. Methods to modify previously default behaviour often have names like `withoutOptionY()` or `withExtraZ()`.
+
+Feel free to create a [new issue](https://github.com/lovell/sharp/issues/new) to gather feedback on a potential API change.
+
+### Remove an existing public method
+
+A method to be removed should be deprecated in the next major version then removed in the following major version.
+
+By way of example, the [bilinearInterpolation method](https://github.com/lovell/sharp/blob/v0.6.0/index.js#L155) present in v0.5.0 was deprecated in v0.6.0 and removed in v0.7.0.
+
+## Run the tests
+
+### Functional tests and static code analysis
+
+```sh
+npm test
+```
+
+### Memory leak tests
+
+Requires _valgrind_.
+
+```sh
+cd sharp/test/leak
+./leak.sh
+```
+
+## Finally
+
+Please feel free to ask any questions via a [new issue](https://github.com/lovell/sharp/issues/new) or contact me by [e-mail](https://github.com/lovell/sharp/blob/master/package.json#L4).