place invocation gls entry

glossary.tex

@@ -139,6 +139,15 @@
   Each spell level in a talisman requires one \glsentrytext{ingredient} aligned to the correct Sphere},
 }
 
+\newglossaryentry{invocation}{
+  name={Invocations},
+  text={Invocation},
+  prefix={an\space},
+  description={are the basic sentence-formulae which define spells.
+  They consist of one to five `descriptors', one action, and a target.
+  For example, `{\sffamily Distant, Wax Air}' spells encourage air at a distance},
+}
+
 \newglossaryentry{artefact}{
   name={Artefacts},
   text={Artefact},