docs: Add migration guide for h rendering registered component (#1927) (#545)

* docs: Add migration guide for `h` rendering registered component (#1927)

* fix: wording and code formatting.

* chore: remove package-lock.json

* fix: `resolveComponent` should within setup/render

* fix: wording inconsistency

Co-authored-by: wuzheqing <[email protected]>

Author: Fiv5

src/guide/migration/render-function-api.md

@@ -128,6 +128,50 @@ In 3.x, the entire VNode props structure is flattened. Using the example from ab
 }
 ```
 
+## Registered Component
+
+### 2.x Syntax
+
+In 2.x, when a component has been registered, the render function would work well when passing the component's name as a string to the first argument:
+
+```js
+// 2.x
+Vue.component('button-counter', {
+  data: () => ({
+    count: 0
+  }),
+  template: `
+    <button @click="count++">
+          Clicked {{ count }} times.
+    </button>
+  `
+})
+
+export default {
+  render(h) {
+    return h('button-counter')
+  }
+}
+```
+
+### 3.x Syntax
+
+In 3.x, with VNodes being context-free, we can no longer use a string ID to implicitly lookup registered components. Instead, we need to use an imported `resolveComponent` method:
+
+```js
+// 3.x
+import { h, resolveComponent } from 'vue'
+
+export default {
+  setup() {
+    const ButtonCounter = resolveComponent('button-counter')
+    return () => h(ButtonCounter)
+  }
+}
+```
+
+For more information, see [The Render Function Api Change RFC](https://github.com/vuejs/rfcs/blob/master/active-rfcs/0008-render-function-api-change.md#context-free-vnodes).
+
 ## Migration Strategy
 
 ### Library Authors

src/guide/render-function.md

@@ -395,7 +395,7 @@ If we're writing a lot of `render` functions, it might feel painful to write som
 
 ```js
 Vue.h(
-  'anchored-heading',
+  Vue.resolveComponent('anchored-heading'),
   {
     level: 1
   },