Added guidelines to bug reporting section of CONTRIBUTING.

CONTRIBUTING.md

@@ -2,12 +2,18 @@
 
 ## How to report a bug?
 
-* The revision number of three.js
+* Tell us the revision number of three.js you use.
+* Try checking your application with the latest `dev` branch version of three.js (often problems are already fixed there). See [migration guide](https://github.com/mrdoob/three.js/wiki/Migration).
 * Tell us where did you observe the problem: your browser version, your operating system, your graphics card (for example Chrome 23.0.1271.95, Windows 7, Nvidia Quadro 2000M)
 * If you can, try to check your problem on multiple browsers / multiple computers (if you are on Windows, especially helpful is to [compare ANGLE and OpenGL renderers](https://github.com/mrdoob/three.js/wiki/How-to-use-OpenGL-or-ANGLE-rendering-on-Windows))
-* Identify the problem. Saying "it doesn't work" doesn't help much.
-* A small testcase (big chance is that when you do this, you'll find the answer yourself).
+
+* Describe the problem in details (what you get instead of what's expected). Saying "it doesn't work" doesn't help much.
+* Create a small testcase (big chance is when you do this, you'll find the answer yourself).
+* If small testcase is not possible, at least include a link to online live version of your application.
+* If your problem creates some visual glitch it helps to include a screenshot (highlight problematic area if problem is subtle).
+
 * What did you try already?
+* Search issue tracker for similar issues. Somebody else may have already filled an issue about your problem (in that case make a comment there instead of creating new issue). Or there may be other issues that seem similar, it helps if you can cross-reference them (mentioned in text hashed issue number like this `#1234`).
 
 ## How to contribute to three.js?