(DOCSP-37116) Clarify login restrictions (#49)

Author: zach-carr

source/atlas-access.txt

@@ -63,7 +63,8 @@ Account Limitations
   receive an activation code from MongoDB Sales or be invited to an 
   existing organization.
 
-- You cannot use Google SSO credentials to sign up or log in.
+- You cannot sign up or log in with third-party accounts, 
+  such as Google, GitHub, Apple, or Facebook credentials.
 
 Account Security
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