Doc: Acknowledge historically supported CPUs and OSes.

PostgreSQL/POSTGRES has run on a huge range of CPUs and OSes.  As we're
dropping some of the earliest systems the project was founded on, let's
provide a place to remember them.

Discussion: https://postgr.es/m/959917.1657522169%40sss.pgh.pa.us

Author: macdice

doc/src/sgml/installation.sgml

@@ -2153,6 +2153,14 @@ export MANPATH
    <email>pgsql-hackers@lists.postgresql.org</email> is the appropriate place
    to discuss that.
   </para>
+
+  <para>
+   Historical versions of <productname>PostgreSQL</productname> or POSTGRES
+   also ran on CPU architectures including Alpha, Itanium, M32R, M68K,
+   M88K, NS32K, SuperH, and VAX, and operating systems including 4.3BSD, BEOS,
+   BSD/OS, DG/UX, Dynix, HP-UX, IRIX, NeXTSTEP, QNX, SCO, SINIX, Sprite, SunOS,
+   Tru64 UNIX, and ULTRIX.
+  </para>
  </sect1>
 
  <sect1 id="installation-platform-notes">