Rename links for 271 as 272

I had originally intended to publish these last week, but never got
around to it. I'm going to publish them this week instead so am
renaming them to week 272.
Rename notes for week 270 to 271

Last week (beginning 24th Mar) was GFR's week 271. I'd got us in a
muddle when I accidentally overwrote our notes for week 269 in
325bbd753246f857e51f8beb2d3a7af2d5eaf3ec.
Copy notes for week 269 to 270

I've just realised that I overwrote our notes for week 269, with those
for week 270, in commit 325bbd753246f857e51f8beb2d3a7af2d5eaf3ec. I'm
duplicating the notes here so that I can then revert that erroneous
commit.

I've updated the page title to reflect the fact that these notes are
for week 270.
Revert "Add notes for week 270"

This reverts commit 325bbd753246f857e51f8beb2d3a7af2d5eaf3ec.

I accidentally overwrote our notes for week 269 when I added the notes
for week 270. I've since taken a copy of the actual week 270 notes and
am now reverting this commit to undo the damage.