docs: add installation guide to README.md

Author: Ryoga-exe

README.md

@@ -15,3 +15,25 @@ Automatically generated API Reference for the project can be found at https://re
 > [!NOTE]
 > Zig autodoc is in beta;
 > the website may be broken or incomplete.
+
+## Installation
+
+Add `ac-library-zig` package to your `build.zig.zon` by following command:
+
+```shell
+# Use tagged release of ac-library-zig
+# Replace `<REPLACE ME>` with the version of ac-library-zig that you want to use
+# See: https://github.com/Ryoga-exe/ac-library-zig/releases
+zig fetch --save=ac-library git+https://github.com/Ryoga-exe/ac-library-zig#<REPLACE ME>
+
+# Use latest build of master branch
+zig fetch --save=ac-library git+https://github.com/Ryoga-exe/ac-library-zig
+```
+
+You can then import `ac-library` in your `build.zig` with:
+
+```zig
+const ac_library = b.dependency("ac-library", .{});
+const exe = b.addExecutable(...);
+exe.root_module.addImport("ac-library", ac_library.module("ac-library"));
+```