[indirectcallable.traits] Clarify template vs specialization

This is a fix for the wording in paper P2609R3.

The template is distinct from its specialization, and
"indirect-value-t<T>" is not "the exposition template".

Author: burblebee

source/iterators.tex

@@ -2419,7 +2419,8 @@
 \pnum
 To implement algorithms taking projections,
 it is necessary to determine the projected type of an iterator's value type.
-The exposition-only alias template \tcode{\exposid{indirect-value-t}<T>} denotes
+For the exposition-only alias template \exposid{indirect-value-t},
+\tcode{\exposid{indirect-value-t}<T>} denotes
 \begin{itemize}
 \item
 \tcode{invoke_result_t<Proj\&, \exposid{indirect-value-t}<I>>}