Update README.md

Insertion of data code was not correct due to a copy paste error.

Author: taloglu

Diff for: README.md

@@ -121,7 +121,7 @@ from supabase_py import create_client, Client
 url: str = os.environ.get("SUPABASE_TEST_URL")
 key: str = os.environ.get("SUPABASE_TEST_KEY")
 supabase: Client = create_client(url, key)
-data = supabase.table("countries").select("*").execute()
+data = supabase.table("countries").insert({"name":"Germany"}).execute()
 assert len(data.get("data", [])) > 0
 ```