Adds demo.

README.md

@@ -1,2 +1,27 @@
 # zig-args
 Simple-to-use argument parser with struct-based config
+
+```zig
+const options = try argsParser.parse(struct {
+    // This declares long options for double hyphen
+    output: ?[]const u8 = null,
+    @"with-offset": bool = false,
+    @"with-hexdump": bool = false,
+    @"intermix-source": bool = false,
+    numberOfBytes: ?i32 = null,
+
+    // This declares short-hand options for single hyphen
+    pub const shorthands = .{
+        .S = "intermix-source",
+        .b = "with-hexdump",
+        .O = "with-offset",
+        .o = "output",
+    };
+}, &args, argsAllocator);
+defer options.deinit();
+
+std.debug.warn("parsed result:\n{}\npositionals:\n", .{options.options});
+for (options.args) |arg| {
+    std.debug.warn("\t{}\n", .{arg});
+}
+```

demo.zig

@@ -13,12 +13,14 @@ pub fn main() !void {
     defer argsAllocator.free(exeName);
 
     const options = try argsParser.parse(struct {
+        // This declares long options for double hyphen
         output: ?[]const u8 = null,
         @"with-offset": bool = false,
         @"with-hexdump": bool = false,
         @"intermix-source": bool = false,
         numberOfBytes: ?i32 = null,
 
+        // This declares short-hand options for single hyphen
         pub const shorthands = .{
             .S = "intermix-source",
             .b = "with-hexdump",