added header docstring to '_api.py'

Author: iLLiCiTiT

ayon_api/_api.py

@@ -1,3 +1,11 @@
+"""Singleton based server api for direct access.
+
+This implementation will be probably the most used part of package. Gives
+option to have singleton connection to Server URL based on environment variable
+values. All public functions and classes are imported in '__init__.py' so
+they're available directly in top module import.
+"""
+
 import os
 import socket