README.md not up-to-date

[ctmbl]

The README.md is missleading the user, we can read:
in Usage section

api = HaApiV5(
        api_base='api.helloasso.com',
        client_id=XXXXXX,
        client_secret=XXXXXX,
        timeout=60
    )

And
in Usage Exemple section

api = ApiV5(
        api_base='api.helloasso.com',
        client_id=XXXXXX,
        client_secret=XXXXXX,
        timeout=60
    )

api.call("url", method="POST", data={...})

Two different names are given ApiV5 and HaApiV5 for the main class, I found out that HaApiV5 was the right one

In Authorization section
We can read

from apiv5 import ApiV5

Where, from my experience, it should be,

from helloasso_api import HaApiV5

[ctmbl]

I could propose a PR to update the documentation if you wish!