Updated contributing.md + added coding guideline

Author: Geolim4

.github/CONTRIBUTING.md

@@ -16,11 +16,4 @@ resolved in a timely manner.
 Contributing policy
 -------------------
 
-Fork the project, create a feature branch, and send us a pull request.
-
-To ensure a consistent code base, you should make sure the code follows
-the [PSR-2 Coding Standards](http://www.php-fig.org/psr/psr-2/). You can also
-run [php-cs-fixer](https://github.com/FriendsOfPHP/PHP-CS-Fixer) with the
-configuration file that can be found in the project root directory.
-
-If you would like to help, take a look at the [list of open issues](https://github.com/PHPSocialNetwork/phpfastcache/issues).
+Our contributing policy is described in our [Coding Guideline](https://github.com/PHPSocialNetwork/phpfastcache/blob/v7/CODING_GUIDELINE.md)

CODING_GUIDELINE.md

@@ -0,0 +1,25 @@
+CODING GUIDELINE
+-------------------
+
+Fork the project, create a feature branch, and send us a pull request.
+Preferably on a distinct branch.
+
+To ensure a consistent code base, you should make sure the code follows
+the [PSR-2 Coding Standards](http://www.php-fig.org/psr/psr-2/). You can also
+run [php-cs-fixer](https://github.com/FriendsOfPHP/PHP-CS-Fixer) with the
+configuration file that can be found in the project root directory.
+
+If you would like to help, take a look at the [list of open issues](https://github.com/PHPSocialNetwork/phpfastcache/issues).
+
+PHPFASTCACHE's specialties 
+-------------------
+As of the V7 your contributions MUST comply the following standards:
+
+- **PHP CORE FUNCTIONS**
+  - To improve opcode efficiency, you MUST prefix core function by a '\\'
+    - E.g: `$var = \str_replace('value', '', $var);`
+- **PHP CORE CLASSES**
+  - Do not imports non-namespaced classes, use an absolute path instead:  
+    - E.g: `$date = new \DateTime();`
+
+This list is non-exhaustive and will may subject to evolve at any time.