Tweak day 1 code structure

day1/src/main.zig

@@ -5,12 +5,13 @@ pub fn main() anyerror!void {
     defer arena.deinit();
     const alloc = &arena.allocator;
 
-    // Part 1
+    // Read our input
     var f = try std.fs.cwd().openFile("input", .{});
     defer f.close();
     var contents = try f.readToEndAlloc(alloc, std.math.maxInt(u32));
     defer alloc.free(contents);
 
+    // Part 1
     var depths = std.ArrayList(u32).init(alloc);
     defer depths.deinit();