fix build pkg (#14)

README.md

@@ -8,6 +8,21 @@ See https://github.com/microsoft/uf2#file-containers for how we're going to embe
 
 For use in a build.zig:
 
+```zig
+const uf2 = @import("uf2");
+
+pub fn build(b: *Build) void {
+    // ...
+    const uf2_dep = b.dependency("uf2", .{});
+
+    const uf2_file = uf2.from_elf(uf2_dep, exe, .{ .family_id = .RP2040 });
+    _ = b.addInstallFile(uf2_file, "bin/test.uf2");
+}
+
+```
+
+# Manually Executing elf2uf2
+
 ```zig
 pub fn build(b: *Build) void {
     // ...

build.zig

@@ -5,7 +5,7 @@ const FileSource = std.Build.FileSource;
 
 const uf2 = @import("src/uf2.zig");
 
-pub fn from_elf(dep: Dependency, exe: CompileStep, opts: uf2.Options) FileSource {
+pub fn from_elf(dep: *Dependency, exe: *CompileStep, opts: uf2.Options) FileSource {
     std.debug.assert(!opts.bundle_source); // TODO: bundle source in UF2 File
     const b = dep.builder;
     const elf2uf2 = dep.artifact("elf2uf2");