Elaborate median and percentile info in verbose output

[silvenon]

I'm slightly ashamed to admit that I don't know what this means:

Median mobile site image weight
17 kB

nor this:

+4.59 MB compared to sites in the 25th percentile

The --verbose output could perhaps elaborate that part? I could submit a PR, I just don't know what this output means and would appreciate pointers. 😅 I read #8, but it didn't help me fully understand.

[silvenon]

In the meantime, let me take a guess. The median output I don't think I understand, but here's my guess about the percentile output. This:

+4.59 MB compared to sites in the 25th percentile

roughly translates to:

4.59 MB more than the max image weight of the top 25% pages in terms of low image weight