docs: update behavior difference

Author: yyx990803

README.md

@@ -310,12 +310,10 @@ Check out the [examples directory](https://github.com/vuejs/petite-vue/tree/main
 
 ### Has Different Behavior
 
-- Most expressions (except for structural directives like `v-if` and `v-for`) has access to the following magic properties:
-  - `$el`
-  - `$nextTick`
-- `createApp()` (accepts global state instead of root component)
-- Components
-- Custom directives
+- In expressions, `$el` points to the current element the directive is bound to (instead of component root element)
+- `createApp()` accepts global state instead of a component
+- Components are simplified into object-returning functions
+- Custom directives have a different interface
 
 ### Vue Compatible
 
@@ -385,4 +383,4 @@ This is also how Vue 1 worked. The trade-off here is that this approach is coupl
 
 ## License
 
-MIT
+MIT