docs(vue): add vuejs usage docs

core/src/components/modal/usage/vue.md

@@ -0,0 +1,62 @@
+```vue
+<template>
+  <div>
+    <ion-header>
+      <ion-toolbar>
+        <ion-title>{{ title }}</ion-title>
+      </ion-toolbar>
+    </ion-header>
+    <ion-content padding>
+      {{ content }}
+    </ion-content>
+  </div>
+</template>
+
+<script>
+export default {
+  name: 'Modal',
+  props: {
+    title: { type: String, default: 'Super Modal' },
+  },
+  data() {
+    return {
+      content: 'Content',
+    }
+  },
+}
+</script>
+```
+
+```vue
+<template>
+  <ion-page class="ion-page" main>
+    <ion-content class="ion-content" padding>
+      <ion-button @click="openModal">Open Modal</ion-button>
+    </ion-content>
+  </ion-page>
+</template>
+
+<script>
+import Modal from './modal.vue'
+
+export default {
+  methods: {
+    openModal() {
+      return this.$ionic.modalController
+        .create({
+          component: Modal,
+          componentProps: {
+            data: {
+              content: 'New Content',
+            },
+            propsData: {
+              title: 'New title',
+            },
+          },
+        })
+        .then(m => m.present())
+    },
+  },
+}
+</script>
+```