docs: update identity.ID field documentation

See #956

identity/identity.go

@@ -27,10 +27,10 @@ type (
  Identity struct {
  l *sync.RWMutex `db:"-" faker:"-"`
 
- // ID is a unique identifier chosen by you. It can be a URN (e.g. "arn:aws:iam::123456789012"),
- // a stringified integer (e.g. "123456789012"), a uuid (e.g. "9f425a8d-7efc-4768-8f23-7647a74fdf13"). It is up to you
- // to pick a format you'd like. It is discouraged to use a personally identifiable value here, like the username
- // or the email, as this field is immutable.
+ // ID is the identity's unique identifier.
+ //
+ // The Identity ID can not be changed and can not be chosen. This ensures future
+ // compatibility and optimization for distributed stores such as CockroachDB.
  //
  // required: true
  ID uuid.UUID `json:"id" faker:"-" db:"id"`