Documentation update

[glebmlk]

Please update documentation or code examples about using angular events with map #id.
So that, if you have provided YOUR_MAP_ID with leaflet

<leaflet id="YOUR_MAP_ID" lf-draw="drawOprions"></leaflet>

you need to add YOUR_MAP_ID to events subscribtion e.g.

$scope.$on('leafletDirectiveDraw.' + YOUR_MAP_ID + '.' + eventName, function handler(e, args));

[nmccready]

Please make a PR and make the appropriate changes to the Readme.md .