Improve readme (generation of keys)

[jmMeessen]

Based on my difficulties to use the OVH provider I proposed some improvements to the readme on Terraform registry. It solves issue #161 and #9.

I describe how to retrieve the API keys and re-ordered the description about its use in the configuration.

Note that the english speaking documentation (the only one I found via Google) do barely help. The French speaking one is much better.

I wonder if there shouldn't be a hint to use the Use Provider button to generate the required providers block. Newcomers might not be familiar with the use non-official providers.

[yanndegat]

Hi @jmMeessen

thank you very much for your contribution

it will improve the usability of the provider. thanks