chore(input-datepicker): added readme file

packages/input-datepicker/README.md

@@ -0,0 +1,40 @@
+# Input Datepicker
+
+`lion-input-datepicker` component is based on the date text input field. Its purpose is to provide a way for users to fill in a date with a datepicker.
+For an input field with a big range, such as `birthday-input`, a datepicker is not the ultimate tool, so use the standard [lion-input-date](../input-date).
+
+## Features
+- input field with a datepicker to help to choose a date
+- based on [lion-input-date](../input-date)
+- makes use of [lion-calendar](../calendar) inside the datepicker
+- makes use of [formatDate](../localize/docs/date.md) for formatting and parsing.
+- option to overwrite locale to change the formatting and parsing
+- can make use of date specific [validators](../validate/docs/DefaultValidators.md) with corresponding error messages in different languages
+  - isDate (default)
+  - minDate
+  - maxDate
+  - minMaxDate
+  - isDateDisabled
+
+## How to use
+
+### Installation
+```
+npm i --save @lion/input-datepicker
+```
+
+```js
+import '@lion/input-datepicker/lion-input-datepicker.js';
+
+// validator import example
+import { minDateValidator } from '@lion/validate';
+```
+
+### Example
+
+```html
+<lion-input-datepicker
+  name="date"
+  .errorValidators="${[['required'], minDateValidator(new Date('2019/06/15'))]}"
+></lion-input-datepicker>
+```