[CIAMP-1708] Update documentation around IdP login (#159)

Update the documentation to reflect that IdP-initiated login is now supported

Author: emilywoods

docs/guides/modules/permissions-authentication/pages/sign-in-to-an-sso-enabled-organization.adoc

@@ -17,14 +17,13 @@ Once you have a CircleCI account you can join an SSO-enabled CircleCI organizati
 
 * Get xref:manage-roles-and-permissions.adoc#add-people-to-your-organization[an invite].
 * Visit the CircleCI link:https://app.circleci.com/home/[home page]. Select the **Join Organisation** dropdown, and then select the option to **Join via SSO**.
+* Via your organization's Identity Provider (IdP).
 
 [log-in-to-an-organization]
 == Authenticate with SSO for an organization
 
 You must be logged in to your CircleCI account in order to authenticate with SSO for an organization.
 
-If you have authenticated with an SSO-enabled CircleCI organization previously and your session has expired, the next time you attempt to access your organization's resources, you will be redirected to your org's Identity Provider (IdP) to authenticate before being granted access once again.
+If you have authenticated with an SSO-enabled CircleCI organization previously and your session has expired, the next time you attempt to access your organization's resources, you will be redirected to your organization's IdP to authenticate before being granted access once again.
 
 When your session expires, you will be prompted to re-authenticate.
-
-NOTE: Logging in via your Identity Provider (IdP) is not supported. Instead you can bookmark the SSO authentication link. The URL is `\https://circleci.com/authentication/login?f=ssovalidate&organization-id=<organization_id>`, where `organization_id` is the organization ID (a universally unique identifier) that represents your organization. You can find your CircleCI organization ID by navigating to menu:Organization Settings[Overview] in the link:https://app.circleci.com/[CircleCI web app].