[svd_intro] Bold font

Hi @mmcky 

I really like the new bold font. They look wonderful. 

In svd_intro, it seems we may overusing them.  

For example in section 5.2, with 14 sentences, we have 12 bold phrases, in which SVD is bolded 3 times repeatedly.

Would it make sense to reduce some of the repetition?

Best,
Longye