Add more install docs

docs/narr/install/prereqs.rst

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+
+Prerequisites
+=============
+
+Wuttjamaican requires Python, and optionally a database of some sort.
+
+
+Python
+------
+
+Currently at least Python 3.6 is required, however:
+
+As of writing only Python 3.8 and newer are supported by the official
+Python team, so that is strongly recommended.  It is likely that will
+soon become the minimum requirement for WuttJamaican as well.
+
+Also note, Python 3.11 is the newest version being tested so far.
+
+See also https://endoflife.date/python
+
+
+Database
+--------
+
+There is not yet much logic in WuttJamaican which pertains to the
+:term:`app database` so we will not document much about that here
+either.
+
+For now just know that in a production environment, PostgreSQL is
+recommended for the DB backend.  So install that if you want to be
+certain of a good experience.
+
+But technically speaking, anything supported by `SQLAlchemy`_ should
+work.  See also :doc:`/narr/config/table`.
+
+.. _SQLAlchemy: https://www.sqlalchemy.org