Add more complete usage documentation in README

README.md

@@ -4,3 +4,83 @@
 [![docs](https://github.com/dlozeve/ShaderTool/actions/workflows/docs.yml/badge.svg)](https://dlozeve.github.io/ShaderTool/)
 
 Live tool for developing OpenGL shaders interactively.
+
+I developed this small program to experiment with shaders locally, to
+reproduce an experience like [Shadertoy](https://www.shadertoy.com/)
+offline, with the ability to choose my own text editor. It was also a
+good project to learn OpenGL development. For this reason, the code is
+very minimal and should be fairly readable.
+
+Additional features:
+
+- Extensive logging (using the nice
+  [log.c](https://github.com/rxi/log.c) library)
+- FPS tracking
+- Reload shaders automatically on save (using
+  [inotify](https://man.archlinux.org/man/inotify.7))
+- Save screenshot to a file
+- Complete argument parsing with
+  [Argp](https://www.gnu.org/software/libc/manual/html_node/Argp.html)
+- Full documentation with [Doxygen](https://www.doxygen.nl/index.html)
+
+## Build
+
+This project requires the [GLFW](https://www.glfw.org/),
+[GLEW](http://glew.sourceforge.net/), and
+[FreeImage](https://freeimage.sourceforge.io/) libraries. On a
+Debian/Ubuntu system:
+```sh
+sudo apt-get install libglfw3-dev libglew-dev libfreeimage-dev
+```
+
+To build (with [Meson](https://mesonbuild.com/)):
+```sh
+meson build
+ninja -C build
+```
+
+To build the documentation with
+[Doxygen](https://www.doxygen.nl/index.html):
+```sh
+doxygen Doxyfile
+```
+
+The documentation is also available
+[online](https://dlozeve.github.io/ShaderTool/).
+
+## Usage
+
+```
+Usage: shadertool [OPTION...] SHADER
+                                    Compile and render the SHADER.
+ShaderTool -- Live tool for developing OpenGL shaders interactively
+
+  -b, --buffer=FILE          Source file of the buffer fragment shader
+  -r, --auto-reload          Automatically reload on save
+  -s, -q, --silent, --quiet  Don't produce any output
+  -v, --verbose              Produce verbose output
+  -?, --help                 Give this help list
+      --usage                Give a short usage message
+  -V, --version              Print program version
+```
+
+For instance, to run the [mandelbrot](shaders/mandelbrot.frag) shader
+with live reloading on save:
+```sh
+shadertool -r shaders/mandelbrot.frag
+```
+
+Keyboard shortcuts:
+
+- `Escape` to quit
+- `R` to reload the shaders
+- `S` to save a screenshot to the current directory, in a file
+  `shadername_frame_date_time.png`
+
+## Limitations
+
+For now, the "buffer" shader (i.e. the additional shader that renders
+in a texture in another framebuffer) does not work properly. I don't
+understand exactly what's broken, but maybe I'll investigate it more
+closely later. If you have any idea about what went wrong, don't
+hesitate to notify me!