requirements

README.md

@@ -14,6 +14,31 @@ Schema not required in MongoDb, so we dont need to create databases, collections
 * Creating, renaming or deleting fields;
 * Creating, changing or deleting indexes
 
+Requirements
+------------
+
+* PHP 5
+ * PHP 5.3 - PHP 5.6
+ * [PHP Mongo Extension](https://pecl.php.net/package/mongo) 0.9 or above (Some features require >= 1.5)
+* PHP 7 and HHVM
+ * [PHP MongoDB Extension](https://pecl.php.net/package/mongodb) 1.0 or above
+ * [Compatibility layer](https://github.com/alcaeus/mongo-php-adapter). Please, note some [restriontions](#compatibility-with-php-7)
+ * Currently not tested in HHVM
+* Tested over MongoDB v.2.4.12, v.2.6.9, v.3.0.2, v.3.2.10, v.3.3.15, v.3.4.0 (See [Unit tests](#unit-tests))
+* [Symfony Event Dispatcher](http://symfony.com/doc/current/components/event_dispatcher/introduction.html)
+* [GeoJson version ~1.0](https://github.com/jmikola/geojson)
+* [PSR-3 logger interface](https://github.com/php-fig/log)
+<br/>
+<br/>
+
+Compatibility with PHP 7
+------------------------
+
+> PHPMongo currently based on old [ext-mongo](https://pecl.php.net/package/mongo) entension.
+> To use this ODM with PHP 7, you need to add [compatibility layer](https://github.com/alcaeus/mongo-php-adapter), which implement API of old extension over new [ext-mongodb](https://pecl.php.net/package/mongodb).
+> To start using PHPMongo with PHP7, add requirement [alcaeus/mongo-php-adapter](https://github.com/alcaeus/mongo-php-adapter) to composer.
+> Restrictions for using ODM with compatibility layer you can read in [known issues](https://github.com/alcaeus/mongo-php-adapter#known-issues) of original adapter.
+
 Installation
 ------------