add load_dotenv() to ensure environment variables are loaded

This PR adds `load_dotenv()` in the instruction to ensure that environment variables, such as `ES_LOCAL_PASSWORD`, are properly loaded when using the Python Elasticsearch client.

Author: MustaphaU

README.asciidoc

@@ -136,6 +136,8 @@ For example, to connect with the Python `elasticsearch` client:
 import os
 from elasticsearch import Elasticsearch
 
+load_dotenv()
+
 username = 'elastic'
 password = os.getenv('ELASTIC_PASSWORD') # Value you set in the environment variable