extract out new contributing guidelines to CONTRIBUTING.md

CONTRIBUTING.md

@@ -1,3 +1,34 @@
-Since this repo includes a large and diverse number of programming languages, frameworks, editors, and ecosystems, it's *very helpful* if you can provide a link to information supporting your pull request. Up-to-date, canonical documentation that mentions the files to be ignored is best.
+# Contributing guidelines
 
-This ensures we can efficiently go through pull requests and keep quality high.
+We’d love you to help us improve this project. To help us keep this collection
+high quality, we request that contributions adhere to the following guidelines.
+
+- **Provide a link to the application or project’s homepage**. Unless it’s
+  extremely popular, there’s a chance the maintainers don’t know about or use
+  the language, framework, editor, app, or project your change applies to.
+  
+- **Provide links to documentation** supporting the change you’re making.
+  Current, canonical documentation mentioning the files being ignored is best.
+  If documentation isn’t available to support your change, do the best you can
+  to explain what the files being ignored are for.
+  
+- **Explain why you’re making a change**. Even if it seems self-evident, please
+  take a sentence or two to tell us why your change or addition should happen.
+  It’s especially helpful to articulate why this change applies to *everyone*
+  who works with the applicable technology, rather than just you or your team.
+  
+- **Please consider the scope of your change**. If your change specific to a
+  certain language or framework, then make sure the change is made to the
+  template for that language or framework, rather than to the template for an
+  editor, tool, or operating system.
+
+- **Please only modify *one template* per pull request**. This helps keep pull
+  requests and feedback focused on a specific project or technology.
+
+In general, the more you can do to help us understand the change you’re making,
+the more likely we’ll be to accept your contribution quickly.
+
+Please also understand that we can’t list every tool that ever existed.
+Our aim is to curate a collection of the *most common and helpful* templates,
+not to make sure we cover every project possible. If we choose not to
+include your language, tool, or project, it’s not because it’s not awesome.