01-bootsector-barebones: append hexdump analysis

[tai271828]

Appending a tip to suggest readers could verify their compiled binary if they are interested in.

Some more topic may be worthy of discussing. I hope they are not too bike-shedding:

• Is appending this kind of information too much detailed? If yes, feel free to reject my pull request.
• Should the tutorial explain a bit the output of hexdump
• Should the tutorial also suggest use the other tool like od to dump the hexadecimal information?