modified the README to include the mapper informations
modified the README to include the mapper informations

Krienas/orientdb-php-odm,ruleant/orientdb-odm,doctrine/orientdb-odm,orientechnologies/orientdb-php-odm,orientechnologies/orientdb-php-odm,Krienas/orientdb-php-odm,doctrine/orientdb-odm,ruleant/orientdb-odm