doc: Clarify unit of logging for log_temp_files

When the unit is omitted from log_temp_files the value is taken as kb,
but the logged value is also without unit but specified in bytes. This
could cause some confusion, so clarify in the documentation which unit
is used when logging.

Reported-by: iphatiey5eu2au6@pasms.be
Reviewed-by: Bruce Momjian <bruce@momjian.us>
Discussion: https://postgr.es/m/166859439833.632.13122583000472281400@wrigleys.postgresql.org

doc/src/sgml/config.sgml

@@ -7501,7 +7501,7 @@ log_line_prefix = '%m [%p] %q%u@%d/%a '
         Temporary files can be
         created for sorts, hashes, and temporary query results.
         If enabled by this setting, a log entry is emitted for each
-        temporary file when it is deleted.
+        temporary file, with the file size specified in bytes, when it is deleted.
         A value of zero logs all temporary file information, while positive
         values log only files whose size is greater than or equal to
         the specified amount of data.