[GSOC] Blog about week 6

Hello everyone!

Over the last week, I started implementing generation number v2. Based
on the performance numbers and subsequent discussion, we have decided to
use generation data chunk approach, storing topological levels into CDAT
and corrected commit date offsets into GDAT chunk. Do note that we are
maintaining backward compatibility using topological level, not with
monotonic offsets.

I also found a performance regression with `commit-graph write
--reachable --changed_path` that sneaked in along with the patch on
moving generation and graph positions into commit-slab.

https://abhishekkumar2718.github.io/gsoc/2020/07/12/gsoc-week-6.html

https://github.com/gitgitgadget/git/pull/676

Yes, I pushed without signing off or a cover letter. It's still a work
in progress.

Thanks
Abhishek