[time.zone.db.tzdb] Say where we look for time_zones, and avoid

readability problem with 'If a time_zone tz is found' phrasing.

Fixes #3892.

Author: zygoloid

source/time.tex

@@ -8737,14 +8737,14 @@
 \returns
 \begin{itemize}
 \item
-If a \tcode{time_zone} \tcode{tz} is found
+If \tcode{zones} contains an element \tcode{tz}
 for which \tcode{tz.name() == tz_name},
 a pointer to \tcode{tz};
 \item
 otherwise,
-if a \tcode{time_zone_link} \tcode{tz_l} is found
+if \tcode{links} contains an element \tcode{tz_l}
 for which \tcode{tz_l.name() == tz_name},
-then a pointer to the \tcode{time_zone} \tcode{tz}
+then a pointer to the element \tcode{tz} of \tcode{zones}
 for which \tcode{tz.name() == tz_l.target()}.
 \end{itemize}
 \begin{note}