chore: add to SSO FAQ

Author: bvs-langchain

src/langsmith/faq.mdx

@@ -60,6 +60,12 @@ Some identity providers retain the original `User ID` through an email change wh
 2. Change their email address in the IdP
 3. Have them login to LangSmith again via SAML SSO - this will trigger the usual [JIT provisioning](#just-in-time-jit-provisioning) flow with their new email address
 
+Changing email address via SCIM or otherwise is not currently supported for users with multiple linked login methods. This error message is shown: `email update not supported with linked login methods`. For example, if a user previously logged in via email/password or Google social login, and then is added with the same email address via SSO, changing their email address is not supported. This applies to both self-hosted and cloud.
+
+#### *Can I change identity providers?*
+
+Reach out to the LangChain support team at [[email protected]](mailto:[email protected]) for support on migration.
+
 #### *How do I fix "405 method not allowed"?*
 
 Ensure you're using the correct ACS URL: [https://auth.langchain.com/auth/v1/sso/saml/acs](https://auth.langchain.com/auth/v1/sso/saml/acs)