add user account guidelines (#508)
add user account guidelines (#508)

* add user account guidelines

* Update docs/realm_guide.md

Co-authored-by: Weston Haught <048bde6c7b65d4526a6685733dc3ee61b869d452@google.com>

* Update docs/realm_guide.md

Co-authored-by: Weston Haught <048bde6c7b65d4526a6685733dc3ee61b869d452@google.com>

* Update docs/realm_guide.md

Co-authored-by: Weston Haught <048bde6c7b65d4526a6685733dc3ee61b869d452@google.com>

Co-authored-by: Weston Haught <048bde6c7b65d4526a6685733dc3ee61b869d452@google.com>
google/exposure-notifications-verification-server,google/exposure-notifications-verification-server,google/exposure-notifications-verification-server,google/exposure-notifications-verification-server