Calendar: add Calendar component (#14908)

examples/docs/en-US/calendar.md

@@ -0,0 +1,65 @@
+## Calendar
+
+Display date.
+
+### Basic
+
+:::demo Set `value` to specify the currently displayed month. If `value` is not specified, current month is displayed. `value` supports two-way binding.
+```html
+<el-calendar v-model="value">
+</el-calendar>
+
+<script>
+  export default {
+    data() {
+      return {
+        value: new Date()
+      }
+    }
+  }
+</script>
+```
+:::
+
+### Custom Content
+
+:::demo Customize what is displayed in the calendar cell by setting `scoped-slot` named `dateCell`. In `scoped-slot` you can get the date (the date of the current cell), data (including the type, isSelected, day attribute). For details, please refer to the API documentation below.
+```html
+<el-calendar>
+  <!-- Use 2.5 slot syntax. If you use Vue 2.6, please use new slot syntax-->
+  <template
+    slot="dateCell"
+    slot-scope="{date, data}">
+    <p :class="data.isSelected ? 'is-selected' : ''">
+      {{ data.day.split('-').slice(1).join('-') }} {{ data.isSelected ? '✔️' : ''}}
+    </p>
+  </template>
+</el-calendar>
+<style>
+  .is-selected {
+    color: #1989FA;
+  }
+</style>
+```
+:::
+
+### Range
+
+:::demo Set the `range` attribute to specify the display range of the calendar. Start time must be Monday, end time must be Sunday, and the time span cannot exceed two months.
+```html
+<el-calendar :range="['2019-03-04', '2019-03-24']">
+</el-calendar>
+```
+:::
+
+### Attributes
+| Attribute       | Description   | Type      | Accepted Values       | Default  |
+|-----------------|-------------- |---------- |---------------------- |--------- |
+| value / v-model | binding value | Date/string/number | —            | —        |
+| range           | time range, including start time and end time. Start time must be Monday, end time must be Sunday, the time span cannot exceed two months | Array     | —           | —      |
+
+### dateCell scoped slot 参数
+| Attribute       | Description   | Type      | Accepted Values       | Default  |
+|-----------------|-------------- |---------- |---------------------- |--------- |
+| date            | date the cell represents  | Date      | —                     | —        |
+| data            | { type, isSelected, day}. `type` indicates which month the date belongs, optional values are prev-month, current-month, next-month; `isSelected` indicates whether the date is selected; `day` is the formatted date in the format yyyy-MM-dd    | Object      | —           | —      |