Add a link to Joe Hellerstein's paper "Looking Back at Postgres",
which is quite an interesting take on the history of Postgres.
The reference to Appendix E was written when we were still keeping
the entire release-note history there, which we stopped doing some
years ago when the O(N^2) cost of that started to become apparent.
Instead, point to the release note archives on the website.
(This per suggestion from Daniel Gustafsson.)
In passing, move the "ports12" biblioentry to be in alphabetical
order within that section.
Discussion: https://postgr.es/m/3345678.1720071633@sss.pgh.pa.us
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