Added instructions to readme

README.md

@@ -1,4 +1,29 @@
 # spdlog
-This is [spdlog](https://github.com/gabime/spdlog), packaged for [Zig](https://ziglang.org/).
+This is [spdlog](https://github.com/gabime/spdlog), packaged for [Zig](https://ziglang.org/). (Intended for C++ projects using Zig as a build tool.)
 
-Usage instructions to be added. Hopefully this things works. :)
+## Usage
+First, update your `build.zig.zon`:
+```sh
+zig fetch --save git+https://github.com/jessechounard/spdlog
+```
+
+Next, in your `build.zig`, you can access the library as a dependency:
+```zig
+const spdlog_dep = b.dependency("spdlog", .{
+    .target = target,
+    .optimize = optimize,
+});
+const spdlog_lib = spdlog_dep.artifact("spdlog");
+
+exe.root_module.linkLibrary(spdlog_lib);
+```
+
+Finally, in your C++ file, you can use the library:
+```cpp
+#include <spdlog/spdlog.h>
+
+int main() {
+  spdlog::info("Hello, world (from spdlog)!");
+  return 0;
+}
+```