* guix/scripts/package.scm (find-packages-by-description): Rewrite to
compute a score based on the number of regexps matched and the number of
matches for each regexp.  Sort according to this score and return it as
a second value.
(process-query) <'search>: Capture the two return values of
'find-packages-by-description'.  Pass #:extra-fields to
'package->recutils'.
* doc/guix.texi (Invoking guix package): Mention relevance, give an
example.