update contributing file

CONTRIBUTING

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-# PR Against the Correct Branch!
-
-Amp development spans two primary branches. PHP 5.x compatibility takes
-place in the v1.0.x branch. All contributions to this branch must
-retain compatibility with PHP 5.5+. The master branch supports only PHP7+
-and is aliased as v1.1.0-dev . Please submit PRs against the appropriate
-branch.
-
-## Licensing 
-
-Any contribution intentionally submitted for inclusion in the Amp project
-shall be under the terms and conditions of the MIT License, without any
-additional terms or conditions. Not withstanding the above, nothing herein
-shall supersede or modify the terms of any separate license agreement you
-may have executed with the Amp project (or its licensor Daniel Lowrey)
-regarding such contributions.

CONTRIBUTING.md

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+## Submitting useful bug reports
+
+Please search existing issues first to make sure this is not a duplicate.
+Every issue report has a cost for the developers required to field it; be
+respectful of others' time and ensure your report isn't spurious prior to
+submission. Please adhere to [sound bug reporting principles](http://www.chiark.greenend.org.uk/~sgtatham/bugs.html).
+
+## Development ideology
+
+Truths which we believe to be self-evident:
+
+- **It's an asynchronous world.**  Be wary of anything that undermines
+   async principles.
+
+- **The answer is not more options.**  If you feel compelled to expose
+   new preferences to the user it's very possible you've made a wrong
+   turn somewhere.
+
+- **There are no power users.** The idea that some users "understand"
+   concepts better than others has proven to be, for the most part, false.
+   If anything, "power users" are more dangerous than the rest, and we
+   should avoid exposing dangerous functionality to them.
+
+## Code style
+
+The amphp project adheres to the PSR-2 style guide with the exception that
+opening braces for classes and methods must appear on the same line as
+the declaration:
+
+https://github.com/php-fig/fig-standards/blob/master/accepted/PSR-2-coding-style-guide.md