Add missing installHeader call

build.zig

@@ -16,6 +16,7 @@ pub fn build(b: *std.Build) !void {
         .optimize = optimize,
     });
     setupFlecs(lib);
+    lib.installHeader("libs/flecs/flecs.h", "flecs.h");
     b.installArtifact(lib);
 
     const main_tests = b.addTest(.{