updated readme file

readme.md

@@ -83,15 +83,29 @@ you don't set a clipping area, you will end with data from all over the world.
 
 ### Clipping
 
+Imposm support importing limiting the features to be imported using a geojson file. 
+This is always desirable to limit the features being imported into the database rather 
+than clipping them.
+
+**NB:** Ensure you add a geojson covering the area you intent to clip into the clip folder.
+
 You can put a shapefile in the clip folder. This shapefile will be 
 used for clipping every features after the import.
 This file has to be named 'clip.shp' and in the CRS you are using in the database (4326 by default).
-When the database container is running, import the shapefile in the database using the command : 
+The docker compose uses dependency links which ensures that the database is started first before
+imposm the script now imports the shapefile into the database when the imposm container starts.
+
+If you add the `clip.shp` file after the containers has started you can still import the 
+shp using the provided makefile with the command:
 
 `make import_clip`.
 
 You can remove the clip file : `make remove_clip`.
 
+**NB:** It is encouraged to simplify the geometry for the `clip.shp` or `clip.geojson` as
+a simplified geometry is easier to process during the import or clipping. Rather use the 
+minimum bounding box for the area you intent to clip your dataset with.
+
 ### QGIS Styles
 
 The database is provided with some default styles. These styles will be loaded