Documentation: Add more intro for "boundsElementSelector" and "offsetTopPad" on readme

[xjxxjx1017]

I was using .js file as the reference. I didn't notice that I could use prop - "boundsElementSelector" and "offsetTopPad" to customize some necessary functions, until I read the .vue code.
Maybe a bit more introductions for them on the main page?

Thanks for the very good stuff by the way.

Cheers,
Jackson

[quinnlangille]

Hey @xjxxjx1017, there currently isn't anyone actively maintaining this package. However, I agree we need a documentation update - I'll see what I can do in my free time in the next week or two. Thanks for the suggestion