readme: Add installation section

README.md

@@ -115,10 +115,49 @@ pub fn main() !void {
 
 </details>
 
+## Installation
+
+1. Declare Getty as a project dependency with `zig fetch`:
+
+    ```sh
+    # Latest version
+    zig fetch --save git+https://github.com/getty-zig/getty.git#master
+
+    # Specific version
+    zig fetch --save git+https://github.com/getty-zig/getty.git#<COMMIT>
+    ```
+
+2. Expose Getty as a module in your project's `build.zig`:
+
+    ```zig
+    pub fn build(b: *std.Build) void {
+        const target = b.standardTargetOptions(.{});
+        const optimize = b.standardOptimizeOption(.{});
+
+        const opts = .{ .target = target, .optimize = optimize };      // 👈
+        const getty_mod = b.dependency("getty", opts).module("getty"); // 👈
+
+        const exe = b.addExecutable(.{
+            .name = "my-project",
+            .root_source_file = .{ .path = "src/main.zig" },
+            .target = target,
+            .optimize = optimize,
+        });
+        exe.root_module.addImport("getty", getty_mod); // 👈
+
+        // ...
+    }
+    ```
+
+3. Import Getty into your code:
+
+    ```zig
+    const getty = @import("getty");
+    ```
+
 ## Resources
 
 - [Website](https://getty.so/)
-- [Installation](https://getty.so/user-guide/installation/)
 - [Tutorial](https://getty.so/user-guide/tutorial/)
 - [Examples](examples)
 - [API Reference](https://docs.getty.so/)