Update README and dependencies

README.md

@@ -2,6 +2,33 @@
 
 Create a photo mosaic out of any tileset and source image!
 
+## Build
+1. Use [rustup](https://rustup.rs/) to install the rust compiler.
+2. Compile the project with `cargo build -r`. The resulting binary is located in `./target/release/themis`
+3. Run the binary either from the `./target` directory or with `cargo run -r -- -h`
+
 ## Usage
 
-Clone the repo and run `cargo run --release -- -h`, everything will be explained
+### Flags
+- `-h`, `--help`: Prints the help dialog
+- `-k`, `--keep-aspect-ratio`: Keep the aspect ratio of the original image
+- `-V`, `--version`: Print the current version of this program
+
+### Options
+- `-i`, `--input-dir <input-dir>`: Specify the path to the cover images.
+    These images are used to compile a mosaic image from the tiles.
+- `-m`, `--mosaic-size <mosaic-size`: Specify the side length of tiles in the target image.
+    A mosaic therefore consists of `mosaic-size x mosaic-size` tiles. The default value is 128.
+- `-o`, `--output-dir <output-dir`: The output directory where all finished mosaic images will be saved.
+    The default directory is `output`.
+- `--tile-size <tile-size`: The side length of each tile (in pixel). This influences the image resolution inside a tile.
+    The default value is `26`.
+- `-t`, `--tiles-dir <tiles-dir`: The directory which contains the tiles to utilize for the mosaic.
+
+### Examples
+```sh
+cargo run -r -- -t ./mosaic_tiles -o ./mosaic_output -i ./cover_images -m 100 --tile-size 200
+```
+This example will take one or multiple cover images (sequentially) out of the `./cover_images` directory.
+Themis then scales down the tiles out of `./mosaic_tiles` to `200 x 200` pixels and arranges
+the tiles. The result will be a mosaic consisting of `100 x 100` tiles stored in `./mosaic_output`.