[Maps] Add EPSG-code to docs (#58378)

docs/setup/settings.asciidoc

@@ -231,7 +231,7 @@ This setting does not impact <<tilemap, Coordinate map visualizations>> and <<re
 use in <<regionmap, Region Map>> visualizations. Supported on {ece}. Each layer
 object points to an external vector file that contains a geojson
 FeatureCollection. The file must use the
-https://en.wikipedia.org/wiki/World_Geodetic_System[WGS84 coordinate reference system]
+https://en.wikipedia.org/wiki/World_Geodetic_System[WGS84 coordinate reference system (ESPG:4326)]
 and only include polygons. If the file is hosted on a separate domain from
 Kibana, the server needs to be CORS-enabled so Kibana can download the file.
 The following example shows a valid regionmap configuration.

x-pack/legacy/plugins/file_upload/public/components/json_index_file_picker.js

@@ -268,6 +268,10 @@ export class JsonIndexFilePicker extends Component {
                     maxFileSize: bytesToSize(MAX_FILE_SIZE),
                   }}
                 />
+                <br />
+                {i18n.translate('xpack.fileUpload.jsonIndexFilePicker.coordinateSystemAccepted', {
+                  defaultMessage: 'Coordinates must be in EPSG:4326 coordinate reference system.',
+                })}{' '}
               </span>
             )
           }