CHECKLST.txt: suggest writing Windows Store blurb ahead of time.

That's two releases running I've got most of the way through the
mechanical upload processes and suddenly realised I still have a piece
of creative writing to do. A small one, but even so, there's no reason
it couldn't have been prepared a week in advance like the rest of the
announcements and changelogs. The only reason I didn't is that the
checklist didn't remind me to. Now it does.

(cherry picked from commit da550c3158)

CHECKLST.txt

@@ -162,6 +162,15 @@ Preparing to make the release
       enabled), by editing prerel_version() in components/Base.mc to
       return undef.
 
+ - Prepare some 'what's new in this release' blurb for the Windows
+   Store. This should be very brief - even briefer than the website
+   news item. Keep it to a couple of sentences in a single paragraph,
+   templated along the lines of 'X.YZ adds support for this, that and
+   the other, and fixes bugs including this and that', or 'X.YZ is a
+   bug-fix release, mostly in the area of Foo, with one important fix
+   to Bar'.
+    * Might as well check this into putty-aux too.
+
  - Update the wishlist, in a local checkout:
     * If there are any last-minute wishlist entries (e.g. security
       vulnerabilities fixed in the new release), write entries for
@@ -255,7 +264,8 @@ locally, this is the procedure for putting it up on the web.
          listing
        * upload revised screenshots, if necessary
        * update the URL in the "Applicable license terms" box
-    + press Publish to submit that to the actual upload process
+    + press Publish or Submit (or whatever the button is called this
+      time) to submit that to the actual upload process
 
  - Announce the release!
     + Construct a release announcement email whose message body is the