doc(runtime-c-api) Improve the README.md.

lib/runtime-c-api/README.md

@@ -1,10 +1,132 @@
+<p align="center">
+  <a href="https://wasmer.io" target="_blank" rel="noopener noreferrer">
+    <img width="400" src="https://raw.githubusercontent.com/wasmerio/wasmer/master/logo.png" alt="Wasmer logo">
+  </a>
+</p>
+
+<p align="center">
+  <a href="https://circleci.com/gh/wasmerio/wasmer/">
+    <img src="https://img.shields.io/circleci/project/github/wasmerio/wasmer/master.svg" alt="Build Status">
+  </a>
+  <a href="https://github.com/wasmerio/wasmer/blob/master/LICENSE">
+    <img src="https://img.shields.io/github/license/wasmerio/wasmer.svg" alt="License">
+  </a>
+  <a href="https://spectrum.chat/wasmer">
+    <img src="https://withspectrum.github.io/badge/badge.svg" alt="Join the Wasmer Community">
+  </a>
+  <a href="https://crates.io/crates/wasm-bindgen">
+    <img src="https://img.shields.io/crates/d/wasmer-runtime-c-api.svg" alt="Number of downloads from crates.io">
+  </a>
+  <a href="https://docs.rs/wasm-bindgen">
+    <img src="https://docs.rs/wasmer-runtime-c-api/badge.svg" alt="Read our API documentation">
+  </a>
+</p>
+
 # Wasmer Runtime C API
 
-## Generating header files
-Run `make capi` from wasmer project root directory
+Wasmer is a standalone JIT WebAssembly runtime, aiming to be fully
+compatible with Emscripten, Rust and Go. [Learn
+more](https://github.com/wasmerio/wasmer).
+
+This crate exposes a C and a C++ API for the Wasmer runtime.
+
+# Usage
+
+The C and C++ header files can be found in the source tree of this
+crate, respectively [`wasmer.h`][wasmer_h] and
+[`wasmer.hh`][wasmer_hh]. They are automatically generated, and always
+up-to-date in this repository.
+
+Here is a simple example to use the C API:
+
+```c
+#include <stdio.h>
+#include "../wasmer.h"
+#include <assert.h>
+#include <stdint.h>
+
+int main()
+{
+    // Read the Wasm file bytes.
+    FILE *file = fopen("sum.wasm", "r");
+    fseek(file, 0, SEEK_END);
+    long len = ftell(file);
+    uint8_t *bytes = malloc(len);
+    fseek(file, 0, SEEK_SET);
+    fread(bytes, 1, len, file);
+    fclose(file);
+
+    // Prepare the imports.
+    wasmer_import_t imports[] = {};
+
+    // Instantiate!
+    wasmer_instance_t *instance = NULL;
+    wasmer_result_t instantiation_result = wasmer_instantiate(&instance, bytes, len, imports, 0);
+
+    assert(instantiation_result == WASMER_OK);
+
+    // Let's call a function.
+    // Start by preparing the arguments.
+
+    // Value of argument #1 is `7i32`.
+    wasmer_value_t argument_one;
+    argument_one.tag = WASM_I32;
+    argument_one.value.I32 = 7;
+
+    // Value of argumen #2 is `8i32`.
+    wasmer_value_t argument_two;
+    argument_two.tag = WASM_I32;
+    argument_two.value.I32 = 8;
+
+    // Prepare the arguments.
+    wasmer_value_t arguments[] = {argument_one, argument_two};
+
+    // Prepare the return value.
+    wasmer_value_t result_one;
+    wasmer_value_t results[] = {result_one};
+
+    // Call the `sum` function with the prepared arguments and the return value.
+    wasmer_result_t call_result = wasmer_instance_call(instance, "sum", arguments, 2, results, 1);
+
+    // Let's display the result.
+    printf("Call result:  %d\n", call_result);
+    printf("Result: %d\n", results[0].value.I32);
+
+    // `sum(7, 8) == 15`.
+    assert(results[0].value.I32 == 15);
+    assert(call_result == WASMER_OK);
+
+    wasmer_instance_destroy(instance);
+
+    return 0;
+}
+```
+
+# Testing
+
+The tests can be run via `cargo test`, such as:
+
+```sh
+$ cargo test -- --nocapture
+```
+
+To run tests manually, enter the `lib/runtime-c-api/tests` directory
+and run the following commands:
+
+```sh
+$ cmake .
+$ make
+$ make test
+```
+
+
+# License
+
+Wasmer is primarily distributed under the terms of the [MIT
+license][mit-license] ([LICENSE][license]).
 
-## Running tests
-The tests can be run via `cargo test`, E.g. `cargo test -p wasmer-runtime-c-api -- --nocapture`
 
-*Running manually*
-`cmake . && make && make test` from the `lib/runtime-c-api/tests` directory
+[wasmer_h]: ./wasmer.h
+[wasmer_hh]: ./wasmer.hh
+[mit-license]: http://opensource.org/licenses/MIT
+[license]: https://github.com/wasmerio/wasmer/blob/master/LICENSE