Update doctrine.rst

Hello,

I just add env variable for mariadb.

Author: abdounikarim

doctrine.rst

@@ -46,6 +46,9 @@ The database connection information is stored as an environment variable called
     # customize this line!
     DATABASE_URL="mysql://db_user:db_password@127.0.0.1:3306/db_name?serverVersion=5.7"
 
+    # to use mariadb:
+    DATABASE_URL="mysql://db_user:db_password@127.0.0.1:3306/db_name?serverVersion=mariadb-10.5.8"
+
     # to use sqlite:
     # DATABASE_URL="sqlite:///%kernel.project_dir%/var/app.db"