[futures.state] Add \tcode for true

Author: Andreas-Krug

source/threads.tex

@@ -10696,7 +10696,7 @@
 the return object or provider gives up its reference to its shared state; and
 
 \item these actions will not block for the shared state to become ready, except that it
-may block if all of the following are true: the shared state was created by a call to
+may block if all of the following are \tcode{true}: the shared state was created by a call to
 \tcode{std::async}, the shared state is not yet ready, and this was the last reference
 to the shared state.
 \end{itemize}