Clarify the language around External Group membership with SAML SSO to clarify...

Clarify the language around External Group membership with SAML SSO to clarify that this will NOT add users to GitLab Groups.

doc/integration/saml.md

@@ -132,14 +132,17 @@ On the sign in page there should now be a SAML button below the regular sign in
 Click the icon to begin the authentication process. If everything goes well the user
 will be returned to GitLab and will be signed in.
 
-## External Groups
+## Marking Users as External based on SAML Groups
 
 >**Note:**
 This setting is only available on GitLab 8.7 and above.
 
-SAML login includes support for external groups. You can define in the SAML
-settings which groups, to which your users belong in your IdP, you wish to be
-marked as [external](../user/permissions.md).
+SAML login includes support for automatically identifying whether a user should
+be considered an [external](../user/permissions.md) user based on the user's group
+membership in the SAML identity provider. This feature **does not** allow you to
+automatically add users to GitLab [Groups](../user/group/index.md), it simply 
+allows you to mark users as External if they are members of certain groups in the 
+Identity Provider.
 
 ### Requirements