Adding doc about our PSR compliance

Author: lonnieezell

user_guide_src/source/intro/index.rst

@@ -43,4 +43,5 @@ CodeIgniter is right for you if:
 	self
 	requirements
 	credits
+	psr
 

user_guide_src/source/intro/psr.rst

@@ -0,0 +1,43 @@
+**************
+PSR Compliance
+**************
+
+The `PHP-FIG <http://www.php-fig.org/>`_ was created in 2009 to help make code more interoperable between frameworks
+by ratifying Interfaces, style guides, and more that members were free to implement or not. While CodeIgniter is
+not a member of the FIG, we are compatible with a number of their proposals. This guide is meant to list the
+status of our compliance with the various accepted, and some draft, proposals.
+
+**PSR-1: Basic Coding Standard**
+
+This recommendation covers basic class, method, and file-naming standards. Our :doc:`style guide </contributing/styleguide>`
+meets PSR-1 and adds its own requirements on top of it.
+
+**PSR-2: Coding Style Guide**
+
+This PSR was fairly controversial when it first came out. CodeIgniter meets many of the recommendations within,
+but does not, and will not, meet all of them.
+
+**PSR-3: Logger Interface**
+
+CodeIgniter's :doc:`Logger </general/logging>` implements all of the interfaces provided by this PSR.
+
+**PSR-4: Autoloading Standard**
+
+This PSR provides a method for organizing file and namespaces to allow for a standard method of autoloading
+classes. Our :doc:`Autoloader </concepts/autoloader>` meets the PSR-4 recommendations.
+
+**PSR-6: Caching Interface**
+
+CodeIgniter will not be trying to meet this PSR, as we believe it oversteps its needs. The newly proposed
+`SimpleCache Interfaces <https://github.com/dragoonis/fig-standards/blob/psr-simplecache/proposed/simplecache.md>`_
+do look like something we would consider.
+
+**PSR-7: HTTP Message Interface**
+
+This PSR standardizes a way of representing the HTTP interactions. While many of the concepts became part of our
+HTTP layer, CodeIgniter does not strive for compatibility with this recommendation.
+
+---
+
+If you find any places that we claim to meet a PSR but have failed to execute it correctly, please let us know
+and we will get it fixed, or submit a pull request with the required changes.