Added note on tweaking settings and using own map (#602)

README.md

@@ -270,10 +270,20 @@ the `/path/on/host` folder contents look like:
 ├── ops.json
 ├── server.properties
 ├── whitelist.json
+├── worlds
+│   └── ... PLACE MAPS IN THEIR OWN FOLDERS HERE ...
 └── ...
 ```
 
-If you add mods while the container is running, you'll need to restart it to pick those
+Providing a presistent `/data` mount is a good idea, both to persist the game world and to allow for the manual configuration which is sometimes needed.
+
+For instance, imagine a scenario when the initial launch has completed, but you now want to change the worldmap for your server.  
+
+Assuming you have a shared directory to your container, you can then (after first launch) drag and drop your premade maps or worlds into the `\worlds\` directory.  **Note:** each world should be placed in its own folder under the `\worlds\` directory.  
+
+Once your maps are in the proper path, you can then specify which map the server uses by changing the `level-name` value in `server.properties` to match the name of your map.
+
+If you add mods or make changes to `server.properties` while the container is running, you'll need to restart it to pick those
 up:
 
     docker stop mc
@@ -292,6 +302,8 @@ This works well if you want to have a common set of modules in a separate
 location, but still have multiple worlds with different server requirements
 in either persistent volumes or a downloadable archive.
 
+
+
 ### Replacing variables inside configs
 
 Sometimes you have mods or plugins that require configuration information that is only available at runtime.
@@ -391,7 +403,7 @@ secrets:
 The content of `db_password`:
 
     ug23u3bg39o-ogADSs
-
+    
 ## Running a Bukkit/Spigot server
 
 Enable Bukkit/Spigot server mode by adding a `-e TYPE=BUKKIT` or `-e TYPE=SPIGOT` to your command-line.