Update README.md

README.md

@@ -26,4 +26,64 @@ $ make test
 to test the sample images. 
 
 FYI, the test results should look like this:
-![preview](./preview.png)
+![preview](./docs/preview.png)
+
+## Building examples
+
+### hello
+
+Minimal build test. Should write `hello` to the stdout.
+
+```
+$ make examples/hello
+$ examples/hello
+```
+
+### ppm
+
+![example-ppm](./docs/example-ppm.png)
+
+Takes in source/mask bitmap and do the image synthesis operation. The dimensions of the source and mask image should match.
+
+```
+$ make examples/ppm
+$ examples/ppm <source> <mask> <result> <context> <neighbors> <probes>
+```
+
+E.g.
+```
+$ examples/ppm assets/source000.ppm assets/mask000.ppm result000.ppm 1 16 64
+```
+
+NOTE: There is a meaningful correlation between **the quality of opration** and the type of fitting method(**context**) described below. The quality of synthesis operation may vary.
+
+| context | method      | shape      | direction |
+|---------|-------------|------------|-----------|
+| 0       | Patching    | -          | -         |
+| 1       | Shuffle     | Random     | Random    |
+| 2       | Brushfire   | Concentric | Inward    |
+| 3       | Directional | Horizontal | Inward    |
+| 4       | Directional | Vertical   | Inward    |
+| 5       | Brushfire   | Concentric | Outward   |
+| 6       | Directional | Horizontal | Outward   |
+| 7       | Directional | Vertical   | Outward   |
+| 8       | Squeeze     | Concentric | Both      |
+
+### painter
+
+![example-painter](./docs/example-painter.gif)
+
+Interactive painting demo. Performs synthesis operation on-the-fly.
+
+This example requires [SDL2](https://wiki.libsdl.org/Installation) installed on the build machine, otherwise build will not succeed.
+
+`Makefile` tries to locate the SDL2 using `pkg-config` command. If facing errors, be sure to check if SDL2 is installed properly.
+
+```
+$ make examples/painter
+$ examples/painter <source>
+```
+E.g.
+```
+$ examples/painter assets/source001.ppm
+```