Confusing wording about SSO Organisations

On the FAQ section for SSO ([linked here](https://buildkite.com/docs/integrations/sso#frequently-asked-questions-what-happens-if-a-person-leaves-our-company)), the wording around 'Buildkite organisation' is confusing.

A member of our company left and subsequently was removed from the GitHub organisation (which is our SSO provider). I was unsure if I had to remove also from the Buildkite UI.

So I would suggest changing the line to something like: "You will need to manually remove them from your **SSO's provider** organization. After that, the user will be automatically removed the Buildkite User list.".

Open the linked SSO FAQ and review the question about what happens when a person leaves the company. Update the wording so it clearly distinguishes the SSO provider's organization from the Buildkite organization and explains whether manual removal is required; done means the user's removal flow is unambiguous.

Written by the indexing model from the issue text.