Merge pull request #105 from vue-leaflet/update-demo-usage

## Usage

Until the complete documentation is ready, please check the [demo project](https://github.com/vue-leaflet/vue3-demo-project/blob/master/src/App.vue) for example usage.

Until the complete documentation is ready, please check the

[component playground](https://github.com/vue-leaflet/vue-leaflet/tree/master/src/playground/views) examples or the

[demo project](https://github.com/vue-leaflet/vue3-demo-project/blob/master/src/App.vue) for usage with Vue 3.

Most component props mimic the vanilla [Leaflet options](https://leafletjs.com/reference-1.7.1.html) as closely as

possible, and generally remain the same as in their [Vue2Leaflet counterparts](https://vue2-leaflet.netlify.app/components/).

### Working with Leaflet

To avoid these issues, import any Leaflet methods asynchronously in response to the LMap component's `@ready` event:

```vue

<template>

  <l-map>

  <l-map style="height:50vh">

    <l-geo-json :geojson="geojson" :options="geojsonOptions" />

  </l-map>

</template>

<script>

// DON'T load Leaflet components here!

import { LMap, LGeoJson } from "./../../components";

// Its CSS is needed though, if not imported elsewhere in your application.

import "leaflet/dist/leaflet.css"

import { LMap, LGeoJson } from "@vue-leaflet/vue-leaflet";

export default {

  components: {