update U boot

INotWant · INotWant · commit 23d2e322d488 · 2021-04-06T17:06:32.000+08:00
diff --git a/u_boot/README.md b/u_boot/README.md
@@ -38,4 +38,4 @@
 
 ### 原理
 
-请 [参考]()
+请 [参考](https://blog.csdn.net/kiss_xiaojie/article/details/115465005)

Original file line number	Diff line number	Diff line change
`@@ -38,4 +38,4 @@`
`38`	`38`
`39`	`39`	`### 原理`
`40`	`40`
`41`		`-请 [参考]()`
	`41`	`+请 [参考](https://blog.csdn.net/kiss_xiaojie/article/details/115465005)`