Update invitations documentation for new email invitations

README.md

@@ -684,9 +684,15 @@ We use upstream Vault interface directly without any (significant) changes, this
 
 ### Inviting users into organization
 
-The invited users won't get the invitation email, instead all already registered users will appear in the interface as if they already accepted the invitation. Organization admin then just needs to confirm them to be proper Organization members and to give them access to the shared secrets.
+#### With SMTP enabled
 
-Invited users, that aren't registered yet will show up in the Organization admin interface as "Invited". At the same time an invitation record is created that allows the users to register even if [user registration is disabled](#disable-registration-of-new-users). (unless you [disable this functionality](#disable-invitations)) They will automatically become "Accepted" once they register. From there Organization admin can confirm them to give them access to Organization.
+Invited users will receive an email containing a link that is valid for 5 days. Upon clicking the link, users can choose to create an account or log in. New users will need to create a new account; existing users who are being invited to a new organization will simply need to log in. After either step, they will show up as "Accepted" in the admin interface, and will be added to the organization when an orgnization admin confirms them.
+
+#### Without SMTP enabled
+
+The invited users won't get an invitation email; instead all already registered users will appear in the interface as if they already accepted the invitation. Organization admin then just needs to confirm them to be proper Organization members and to give them access to the shared secrets.
+
+Invited users that aren't registered yet will show up in the Organization admin interface as "Invited". At the same time an invitation record is created that allows the users to register even if [user registration is disabled](#disable-registration-of-new-users). (unless you [disable this functionality](#disable-invitations)) They will automatically become "Accepted" once they register. From there Organization admin can confirm them to give them access to Organization.
 
 ### Running on unencrypted connection