Mentioned transparency in SETUP.

SETUP.md

@@ -75,8 +75,11 @@ a basic map to apply only changes to use `mtseeder`:
 
 This contacts the `mtredisalize` server running at localhost port 6379 to fetch the block data from. You will
 need a `colors.txt` to map the block nodes to pixel colors of your map. The repository contains
-[one](https://bitbucket.org/s_l_teichmann/mtsatellite/raw/default/colors.txt). See `mtseeder --help` for
-all options.
+[one](https://bitbucket.org/s_l_teichmann/mtsatellite/raw/default/colors.txt).  
+If you want to have certain nodes to be transparent you can add `-transparent=true` to the
+options. In this case if the colors from colors.txt do have a forth color component with a numerical
+value lower than 255 (e.g 128) the corresponding pixels on the resultung tiles would be transparent.  
+See `mtseeder --help` for all options. 
 
 The `-workers=` option and the `GOMAXPROCS=` environment variable are completely optional but very useful
 to exploit multiple processor cores on your machine. Set `GOMAXPROCS=` to the result of `nproc` and `-workers=`
@@ -103,7 +106,8 @@ in the background. To start `mtwebmapper` use:
       -redis-host=localhost            \
       -workers=2
 
-For the `colors=` options applys the same as said above. The `web-host=` is the interface the
+For the `colors=` options applys the same as said above. You can also add
+`-transparent=true` for transparency as mentioned above. The `web-host=` is the interface the
 server ist listening on. `""` means all interfaces. The port defaults to 8808.
 For a productive setup you may consider running it behind a reverse proxy.  
 `-map=` has to be the same path as used by `mtseeder`.