docs(google-maps): add readme (#29898)

* docs(google-maps/map-advanced-marker): README.md added

* Update README.md

Removed list of inputs and corrected spelling.

* Update README.md

(cherry picked from commit a2dc657)

src/google-maps/map-advanced-marker/README.md

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+# MapAdvancedMarker
+
+The `MapAdvancedMarker` component wraps the [`google.maps.marker.AdvancedMarkerElement` class](https://developers.google.com/maps/documentation/javascript/reference/advanced-markers) from the Google Maps JavaScript API. The `MapAdvancedMarker` component displays a marker on the map when it is a content child of a `GoogleMap` component.
+
+**Note:** Use of `map-advanced-marker` requires a `google-map` with a valid `mapId`.
+
+## Example
+
+```typescript
+// google-map-demo.component.ts
+import {Component} from '@angular/core';
+import {GoogleMap, MapAdvancedMarker} from '@angular/google-maps';
+
+@Component({
+  selector: 'google-map-demo',
+  templateUrl: 'google-map-demo.html',
+  imports: [GoogleMap, MapAdvancedMarker],
+})
+export class GoogleMapDemo {
+  center: google.maps.LatLngLiteral = {lat: 24, lng: 12};
+  zoom = 4;
+  advancedMarkerOptions: google.maps.marker.AdvancedMarkerElementOptions = {gmpDraggable: false};
+  advancedMarkerPositions: google.maps.LatLngLiteral[] = [];
+
+  addAdvancedMarker(event: google.maps.MapMouseEvent) {
+    this.advancedMarkerPositions.push(event.latLng.toJSON());
+  }
+}
+```
+
+```html
+<!-- google-map-demo.component.html -->
+<google-map
+  mapId="yourMapId"
+  height="400px"
+  width="750px"
+  [center]="center"
+  [zoom]="zoom"
+  (mapClick)="addAdvancedMarker($event)">
+    @for (position of advancedMarkerPositions; track position) {
+      <map-advanced-marker [position]="position" [options]="advancedMarkerOptions" />
+    }
+</google-map>
+```