feat: Added minor updates in comments for clarity and proposed some u…

[maxzaikin]

Dear David,

During working on examples provided in your book, I have found that some of the code not work me. Thus I decided to make some minor changes for you to consider them as candidates for updates.
Particularly for this PR, I propose following:

1. Highlight explicitly that some of the constants in the head of the notebook are overlap each-other
2. Improve displaying example with faces, thus only blond-hair celebrities are shown
3. Notify that for some versions of TF extension for checkout may be required to be different, so students should pay attention to the TF error messages
4. Notify students that param 'steps_per_epoch=1' may be wanted to be adjusted as it provide instant inference but terrible results

Best regards,
Maks.

P.S.
Love your book. Thanks a lot and don't stop you doing great :)