Update flex-direction.md

docs/uni-app-x/css/flex-direction.md

@@ -3,10 +3,13 @@
 
 <!-- CSSJSON.flex-direction.description -->
 
+## App平台差异  
+App平台默认值为column
+
 <!-- CSSJSON.flex-direction.syntax -->
 
 <!-- CSSJSON.flex-direction.values -->
 
 <!-- CSSJSON.flex-direction.compatibility -->
 
-<!-- CSSJSON.flex-direction.reference -->
\ No newline at end of file
+<!-- CSSJSON.flex-direction.reference -->