Apply suggestions from code review

Co-authored-by: Olivier Mengué <dolmen@cpan.org>

inky/impression.go

@@ -406,6 +406,8 @@ func (d *DevImpression) resetUC() error {
 }
 
 func (d *DevImpression) resetAC() error {
+	// Reference code: https://github.com/pimoroni/inky/blob/a7d380231cc5fac754243b8d66d2c5674c1bd1ac/inky/inky_ac073tc1a.py#L229
+
 	if err := d.cycleResetGPIO(); err != nil {
 		return err
 	}

inky/types.go

@@ -40,7 +40,7 @@ func (m *Model) Set(s string) error {
 	case "IMPRESSION73":
 		*m = IMPRESSION73
 	default:
-		return fmt.Errorf("unknown model %q: expected PHAT, PHAT2, WHAT, IMPRESSION4 or IMPRESSION57 or IMPRESSION73", s)
+		return fmt.Errorf("unknown model %q: expected PHAT, PHAT2, WHAT, IMPRESSION4, IMPRESSION57 or IMPRESSION73", s)
 	}
 	return nil
 }