doc: added Python3 minimal supported version

Author: cuprumtan

README.md

@@ -8,6 +8,8 @@ Mamonsu is an active agent for Zabbix collecting PostgreSQL instance and operati
 Development version, available on GitHub, released under BSD 3-clause.
 ***
 ## Compatibility
+Python 3.3+  
+
 Supported platforms:
 - Linux;
 - FreeBSD;
@@ -48,7 +50,7 @@ A template generated by Mamonsu must be bound to the Zabbix host to receive and
 Mamonsu can be easily customized. You can configure such parameters as the data collection interval for each plugin (by default it is 60 seconds), the size of the message queue for the Zabbix server, optionally disable/enable various components.
 
 ## Requirements
-Only Python3 and any text editor.
+Only Python3.3+ and any text editor.
 
 ## Features
 ### Metrics