Add API usage sample to README.md.

README.md

@@ -32,6 +32,53 @@ MinGW-w64 based compilation works with `make`, and an MSVC 2013 solution is also
 
 ## Usage
 
+### Using the C++ API
+
+To perform reflection and convert to other shader languages you can use the SPIRV-Cross API.
+For example:
+
+```
+#include "spirv_glsl.hpp"
+#include <vector>
+#include <utility>
+
+extern std::vector<uint32_t> load_spirv_file();
+
+int main()
+{
+	// Read SPIR-V from disk or similar.
+	std::vector<uint32_t> spirv_binary = load_spirv_file();
+
+	spirv_cross::CompilerGLSL glsl(std::move(spirv_binary));
+
+	// The SPIR-V is now parsed, and we can perform reflection on it.
+	spirv_cross::ShaderResources resources = glsl.get_shader_resources();
+
+	// Get all sampled images in the shader.
+	for (auto &resource : resources.sampled_images)
+	{
+		unsigned set = glsl.get_decoration(resource.id, spv::DecorationDescriptorSet);
+		unsigned binding = glsl.get_decoration(resource.id, spv::DecorationBinding);
+		printf("Image %s at set = %u, binding = %u\n", resource.name.c_str(), set, binding);
+
+		// Modify the decoration to prepare it for GLSL.
+		glsl.unset_decoration(resource.id, spv::DecorationDescriptorSet);
+
+		// Some arbitrary remapping if we want.
+		glsl.set_decoration(resource.id, spv::DecorationBinding, set * 16 + binding);
+	}
+
+	// Set some options.
+	spirv_cross::CompilerGLSL::Options options;
+	options.version = 310;
+	options.es = true;
+	glsl.set_options(options);
+
+	// Compile to GLSL, ready to give to GL driver.
+	std::string source = glsl.compile();
+}
+```
+
 ### Creating a SPIR-V file from GLSL with glslang
 
 ```