add glossary entry for zef

Closes #4260

Author: coke

doc/Language/glossary.rakudoc

@@ -307,7 +307,7 @@ sufficiently different from its arguments that op= makes little sense.
 
 The module ecosystem consists of all the published modules available for Raku, which
 can be searched at L<Raku Land|https://raku.land/>. Note that different ecosystems
-based on different technologies exist, but this typically refers to the C<zef>
+based on different technologies exist, but this typically refers to the C<fez>
 ecosystem.
 
 =head1 X<Exegesis|Reference,Exegesis>
@@ -1210,6 +1210,10 @@ See also L<https://www.destroyallsoftware.com/talks/wat>.
 A character or group of blank characters, used to separate words. An
 example is the space character « ».
 
+=head1 X<zef|Reference,zef>
+
+L<zef|https://github.com/ugexe/zef> is a tool to manage Raku module installation.
+
 =head1 X<6model|Reference,6model>
 
 C<6model> is used in the L<MoarVM|/language/glossary#MoarVM>, and provides