docs: update docs

Author: hunterliu1003

docs/content/3.api/2.composables/1.use-modal.md

@@ -28,11 +28,17 @@ import { ModalsContainer } from 'vue-final-modal'
 ```ts
 import { VueFinalModal, useModal } from 'vue-final-modal'
 
-const { open, close, options, patchOptions } = useModal({
-  // `component` is optional and the default value is `<VueFinalModal>`.
-  component: VueFinalModal,
+const { open, close, destroy, options, patchOptions } = useModal({
   // Open the modal or not when the modal was created, the default value is `false`.
   defaultModelValue: false,
+  /**
+   * If set `keepAlive` to `true`: 
+   * 1. The `displayDirective` will be set to `show` by default. 
+   * 2. The modal component will not be removed after the modal closed until you manually execute `destroy()`. 
+   */
+  keepAlive: false,
+  // `component` is optional and the default value is `<VueFinalModal>`.
+  component: VueFinalModal,
   attrs: {
     // Bind props to the modal component (VueFinalModal in this case).
     clickToClose: true,
@@ -49,6 +55,8 @@ const { open, close, options, patchOptions } = useModal({
 open().then(() => { /* Do something after modal opened */ })
 // Close the modal
 close().then(() => { /* Do something after modal closed */ })
+// Destroy the modal manually, it only be needed when the `keepAlive` is set to `true`
+destroy()
 // Checkout the modal options
 options // the state of the dynamic modal