Update documentation

README.md

@@ -19,9 +19,46 @@ the top left tile.
 
 ## Usage
 
-    slicerdicer --help
+    slicerdicer -help
 
-    slicerdicer --filename foo.png --tile-size 256 --concurrency 5
+    slicerdicer -filename large_image.png -tile-size 256 -concurrency 5
+
+## Output filenames
+
+The destination for the tiles can be changed with the `-basename` and
+`-path-template` options. The path template must contain 5 placeholders,
+in the following order:
+
+* `%s` basename, as per `-basename` (default `tile`)
+* `%d` zoom level
+* `%d` 'x' coordinate
+* `%d` 'y' coordinate
+* `%d` file format (jpg or png)
+
+The default template is `%s-%d-%d-%d.%s` which results in a flat structure
+with all files in the current directory.
+
+For example, using `-basename map` and
+`-path-template '%s/zoom-%d/%d-%d.%s'` will result in a file structure like:
+
+    map
+    ├── 0
+    │   └── 0-0.png
+    ├── 1
+    │   ├── 0-0.png
+    │   └── 1-0.png
+    └── 2
+        ├── 0-0.png
+        ├── 0-1.png
+        ├── 1-0.png
+        ├── 1-1.png
+        ├── 2-0.png
+        ├── 2-1.png
+        ├── 3-0.png
+        └── 3-1.png
+
+All tiles in a directory called `map`, with a second level directory for zoom
+level, each file named `x-y.png` within that.
 
 ## Notes
 

main.go

@@ -234,7 +234,6 @@ func tileWorker(jobs <-chan tileJob, results chan<- string) {
 		writer, err := j.output.CreatePathAndFile(output_filename)
 		if err != nil {
 			log.Fatalf("could not create path/file: '%s'", err.Error())
-			panic(err)
 		}
 		if j.format == "png" {
 			err = png.Encode(writer, cropped)