Fix code snippet in "Quick start" section of README

[indeliblecanopus]

Hi,
just a variable name fix for quick start snippet included in your README

from hrflow import Hrflow
client = Hrflow(api_secret="YOUR_API_KEY", api_user="YOU_USER_EMAIL")

# read file from directory (in binary mode)
with open("path_to_file.pdf", "rb") as file_resume_cv:
    # Parse it using this method without reference:
    response = client.profile.parsing.add_file(
        source_key="INSERT_THE_TARGET_SOURCE_KEY",
        profile_file=file_resume_cv,
        sync_parsing=1,  # This is to invoke real time parsing
        # Attach an application tag to the profile to be parsed
        tags=[{"name": "application_reference", "value": "TS_X12345"}],
    )