update README

README.md

@@ -84,6 +84,22 @@ LR0~LR7: F0~F7
 LR8: C8
 ```
 
+### shiftable_register
+
+八位移位寄存器。
+
+```
+K0~K7: D0~D7
+K8: RM
+K9: DM
+K10: LM
+K11: R
+K12: L
+单脉冲: CK
+K13: CLR
+LR0~LR7: Y0~Y7
+```
+
 ### counter_8b_with_input
 
 ```