add Installation guide to README

README.md

@@ -7,6 +7,7 @@
 - Keep to folders that are available on all operating systems
 
 ## API
+
 ```zig
 pub const KnownFolder = enum {
     home,
@@ -42,7 +43,31 @@ pub fn open(allocator: std.mem.Allocator, folder: KnownFolder, args: std.fs.Dir.
 pub fn getPath(allocator: std.mem.Allocator, folder: KnownFolder) Error!?[]const u8;
 ```
 
+## Installation
+
+Initialize a `zig build` project if you haven't already.
+
+```bash
+zig init
+```
+
+Add the `known-folders` package to your `build.zig.zon`.
+
+```bash
+zig fetch --save git+https://github.com/ziglibs/known-folders.git
+```
+
+You can then import `known-folders` in your `build.zig` with:
+
+```zig
+const known_folders = b.dependency("known-folders", .{}).module("known-folders");
+const exe = b.addExecutable(...);
+// This adds the known-folders module to the executable which can then be imported with `@import("known-folders")`
+exe.root_module.addImport("known-folders", known_folders);
+```
+
 ## Configuration
+
 In your root file, add something like this to configure known-folders:
 
 ```zig